Messages of condolence, outrage and defiance over the Paris terrorist attack on a newspaper office spread quickly around the world Wednesday with thousands of people taking to the streets to protest the killings and using the slogan "Je Suis Charlie" on social media. 
 
 The inscription "I am Charlie" is written on the fronthead of a woman as she attends a gathering to pay respect for the victims of a terror attack against a satirical newspaper, in Paris, in Paris, Wednesday,... (Associated Press) 
 
 People hold up pens and a phone screen reading 'I am Charlie' in French as they take part in a vigil of people, including many who were French, to show solidarity with those killed in an attack at the... (Associated Press) 
 
 A woman holds a poster reading 'I am Charlie' with a rose, at a gathering in Nice, southeastern France, to express solidarity with those killed in an attack at the Paris offices of weekly newspaper Charlie... (Associated Press) 
 
 People hold candles during a gathering in support for the victims of a terror shooting in Paris, France, as they gather near EU headquarters in Brussels on Wednesday, Jan. 7, 2015. Masked gunmen shouting... (Associated Press) 
 
 A drawing depicting cartoonist Jean Cabut, left, Charlie Hebdo editor Stephane Charbonnier, center, and cartoonist Georges Wolinski, all three of whom were killed when masked gunmen stormed the Paris... (Associated Press) 
 
 People gather to pay their respects for the victims of a terror attack against a satirical newspaper, in Paris, Wednesday, Jan. 7, 2015. Masked gunmen shouting "Allahu akbar!" stormed the Paris offices... (Associated Press) 
 
 A woman holds up a pen and a phone with a sign on the screen reading "I am Charlie" in French as she takes part in a vigil of people, including many who were French, to show solidarity with those killed... (Associated Press) 
 
 People attend a demonstration in solidarity with those killed in an attack at the Paris offices of weekly newspaper Charlie Hebdo, at the French Consulate in Barcelona, Spain, Wednesday, Jan 7, 2015.... (Associated Press) 
 
 People gather to pay their respects for the victims of a terror attack against a satirical newspaper, in Paris, Wednesday, Jan. 7, 2015. Masked gunmen shouting "Allahu akbar!" stormed the Paris offices... (Associated Press) 
 
 A woman holds a candle as she attends a demonstration in solidarity with those killed in an attack at the Paris offices of weekly newspaper Charlie Hebdo, at the French Consulate in Barcelona, Spain,... (Associated Press) 
 
 A man holds a poster reading 'I am Charlie' as he and others gather to express solidarity with the murdered French journalists in front of the Brandenburg Gate in Berlin, Germany, Wednesday, Jan. 7, 2015.... (Associated Press) 
 
 People gather in solidarity of the victims of a terror attack against a satirical newspaper, in Paris, Wednesday, Jan. 7, 2015. Masked gunmen shouting "Allahu akbar!" stormed the Paris offices of a satirical... (Associated Press) 
 
 Many who poured into Place de la Republique in eastern Paris near the site of Wednesday's noontime attack waved papers, pencils and pens. Journalists led the march but most in the crowd weren't from the media world, expressing solidarity and support of freedom of speech. 
 
 Similar gatherings, including some silent vigils, took place at London's Trafalgar Square, in front of the Brandenburg Gate in Berlin, in Madrid, Brussels, Nice and elsewhere. 
 
 "No matter what a journalist or magazine has to say, even if it is not what the majority of people think, they still have the right to say it without feeling in danger, which is the case today," said Alice Blanc, a London student who is originally from Paris and was among those in the London crowd, estimated in the hundreds. 
 
 Online, the declaration "Je Suis Charlie," or "I Am Charlie," replaced profile pictures on Facebook while Twitter users showed themselves with the slogan on signs with words of support for the 12 victims who were killed at Charlie Hebdo, a weekly newspaper that had caricatured the Prophet Muhammad. 
 
 The "Je Suis Charlie" slogan grew into a trending hashtag on Twitter and spread to Instagram, along with an image of a machine gun with the words "Ceci n'est pas une religion," or "This is not a religion." 
 
 One user on Instagram sent out a simple black-and-white drawing of the Eiffel Tower with the message: "Pray for Paris." Another wrote: "Islam is a beautiful religion. This is not what we see on TV. Terrorists are not real Muslims. #IamCharlie." 
 
 Masked gunmen methodically killed the 12 people, including the newspaper's editor, as they shouted "Allahu akbar!" — or "Allah is the greatest" — while firing, then fleeing in a car. 
 
 The newspaper's depictions of Islam have drawn condemnation and threats before. It was firebombed in 2011 and also satirized other religions and political figures. 
 
 There were also protests in some American cities. 
 
 In San Francisco, hundreds of people held pens, tiny French flags and signs that read "I am Charlie" up in the air outside the French Consulate in the financial district. A handful of the participants lit candles that spell out "Je Suis Charlie," while others placed pens and pencils and bouquets of white carnations and red roses by the consulate's door. 
 
 Julia Olson, of Nimes, France, said she wanted to be in the company of other people after hearing the news. 
 
 "There is nothing we can do but be together," the 26-year-old said. 
 
 Several hundred people gathered in Manhattan's Union Square amid chants of "We are not afraid" and holding signs in English and French saying "We are Charlie." 
 
 In Seattle, about 100 people assembled near the French Consulate office with many holding signs in support of the victims. 
 
 The Newseum in Washington displayed "#JeSuisCharlie" on its atrium screen as a show of support for free expression. 
 
 In Los Angeles, a small group gathered outside a French restaurant with people holding up signs and cell phones that read "Je Sui Charlie" and "I am Charlie." 
 
 About 1,000 people gathered near the European Union's headquarters in Brussels to express sympathy and outrage. In Spain, about 200 people in Madrid gathered outside the French Embassy to voice outrage. Some also held pens in the air and chanted "Freedom of Expression" and "We Are All Charlie." 
 
 In 2004, bombs on rush-hour trains killed 191 people in Madrid in Europe's most deadly Islamic terror attack. 
 
 French students in Stockholm organized about 100 people to lay flowers and candles in front of the French Embassy in Stockholm. 
 
 A handful of women in the swank Roman piazza where the French Embassy is located had "Je suis Charlie" banners taped to their jackets. 
 
 "I still cannot believe what happened," said protester Linda Chille. "It is cruel and very shocking." 
 
 The Newseum in Washington is dedicated to the subject of journalism and planned to project "#JeSuisCharlie" on its atrium screen later Wednesday in a show of support for free expression. 
 
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 Angela Charlton in Paris, Jill Lawless in London, Alan Clendenning in Madrid, David Keyton in Stockholm, Nicole Winfield in Rome, Geir Moulson in Berlin, Raf Casert in Brussels, and Olga R. Rodriguez in San Francisco contributed to this report. ||||| Paris (CNN) Marchers raised pens skyward. They lit candles in the dark. They wrote "liberty" and "free expression" on placards in rallies that came hours after a terror attack killed 12 people Wednesday in Paris. 
 
 As the initial shock wore off, the grand boulevards in most of France's major cities became scenes of mourning and solemn demonstrations, with crowds declaring themselves unbowed by the gunmen 's assault on the offices of the magazine Charlie Hebdo . Four of its cartoonists were among those killed in the gunfire. 
 
 "The world has become so sick that (being a humorist or cartoonist) has become a dangerous profession!" said a poster carried by one woman in a mass of protesters in Paris' Place de la Republique. 
 
 One mourner, Corentin Vacheret, described the slain cartoonists as journalists who "are famous in France, especially among people who value the liberty of expression." 
 
 "The fact that they were killed in the most insane circumstances is just sickening," Vacheret said. "I am not a fan of big protests, but I wanted to express that we are not afraid, that this is not going to make us renounce our liberty of expression." 
 
 Rallies also unfolded Wednesday night in Tours, Toulouse, Brest, Lyon, Rennes and Poitiers, among other cities in France, long regarded as a cradle of democracy and liberty. They were joined by demonstrations elsewhere in Europe, including London, Barcelona, Berlin and Rome. 
 
 The most immediate rallying cry against the attack was "Je Suis Charlie," or "I Am Charlie," in reference to the weekly satirical magazine's title, Charlie Hebdo. 
 
 Another sign at the rally in Place de la Republique declared: "I stand up and I express myself with words because they are still the most beautiful weapon!" 
 
 According to Le Monde newspaper, French police said as many as 15,000 people gathered in the Place de la Republique, which was closed to traffic. 
 
 Demonstrators' candles glowed in the darkness. Marchers were mostly silent for the first hour, Le Monde reporter Maxime Goldbaum tweeted, but then began chanting, "Charlie! Charlie! Charlie!" and "We are Charlie!" 
 
 At another point, the chant became a play on words: "Charlie-Charlie-Charliberte!" 
 
 One student held a sign at the Paris rally saying, "Long live liberty! Long live France! Long live Charlie!" 
 
 Alexis, 23 ans, étudiant en commerce : "Je ne viens jamais aux manifs. Là, je n'ai pas hésité". #CharlieHebdo pic.twitter.com/is5Q77tabb — Maxime Goldbaum (@MaximeGoldbaum) January 7, 2015 
 
 Another student, Sacha, told Le Monde newspaper, "We didn't just come here because of the emotion, but because of the principle. Liberty must be defended." 
 
 Sruthi Gottipati of Paris posted a photograph on her Twitter page of someone lighting a flare at the foot of the monument at Place de la Republique, becoming a mirror image of the nearby statues holding torches. 
 
 Another photograph showed several people in the crowd holding aloft a series of illuminated letters in the darkness that stated in English: "NOT AFRAID." 
 
 Just a few feet away from the main demonstration, the gathering took a more sombre tone. Dozens of people created a shrine of pens and pencils on the paving stones, encircled by tealights and candles. 
 
 Many visitors -- some in tears -- stood or sat quietly, with heads bowed, appearing as if they were trying to understand what happened in an office a few streets away. 
 
 Faycal Haddad, a Muslim, condemns the apparent extreme Islamic attacks. 
 
 Faycal Haddad, a Muslim, carried a homemade sign stating "not in my name, not in the name of my religion." 
 
 "I don't want anyone to say that my kids, someone from my family, is involved -- this is not Islam," Haddad said. "If I thought that this was what Islam was about, I would not be part of it. No religion in the world can authorize anyone to kill. 
 
 "We need to unite against these few people, they are a bacteria, a virus, and we need to find a solution," Haddad added. 
 
 He joined the public outpouring on the spur of the moment, straight from work, without telling his wife or kids, he added. 
 
 "I felt it was my job to be here," he said. He was planning to bring his family to the protest planned for Saturday in Paris, he said. 
 
 Luc Lemoine carries a cartoon of his making. 
 
 Luc Lemoine carried a cartoon of his own making showing a dramatic faceoff between two characters: a masked terrorist with a gun and a balding man with a pencil. 
 
 "The drawings never killed anybody," Lemoine said of the Charlie Hebdo cartoonists. 
 
 "Like everybody, I was shocked about what happened. Everybody here grew up with Charlie Hebdo. It is part of French culture and has been for many years, so I felt it was important to be here," Lemoine said. 
 
 Emmanuel Leger and son Binhkim, 15. 
 
 Emmanuel Leger brought his son Binhkim, 15, to a vigil where both held burning candles. 
 
 "I think today is the day everything changed," the father said. 
 
 "I am an artist, I draw, but just for pleasure, and sometimes my drawings are not politically correct," Leger added. "I wanted my son with me, even if he didn't want to come, I'm sure in several years he will remember this time." 
 
 Parisians used social media to urge people to attend the Place de la Republique vigil, which drew a crowd whose numbers reached several thousand. At times, the gathering was silent, but at other moments, many individuals chanted "freedom of expression" loudly. 
 
 Participants laid down flowers and lit candles in the cold night. By 10 p.m., the crowds began to thin. 
 
 In London, about 700 people gathered at Trafalgar Square in an evening vigil for the French victims. 
 
 Many condemned the attackers. 
 
 "Shame on you, pens versus gun? There's no competition, is there. Shame on you, shame on you," said one man attending the London event. "It's the most cowardly thing you can do." ||||| Tens of thousands of people have been holding silent vigils in Paris and other cities around the world following the gun attack at the French satirical magazine Charlie Hebdo that left 12 people dead. 
 
 Image copyright Getty Images 
 
 An estimated 35,000 people gathered in Paris's Place de la Republique to pay tribute to the victims. Many left candles and piles of pens in small memorials. 
 
 Image copyright EPA 
 
 People holding placards held a silent gathering in Montpellier, southern France. Many held placards saying "Je suis Charlie" (I am Charlie). 
 
 Image copyright Getty Images 
 
 Tablets and mobile phones are also being used to convey the message. 
 
 Image copyright AFP 
 
 Some taking part, such as here in Lyon, held pens aloft as a symbol of press freedom. Others sang the Marseillaise, the French national anthem. 
 
 Image copyright AFP 
 
 Similar vigils have been held in other cities. In London a large crowd gathered in Trafalgar Square. 
 
 Image copyright AP 
 
 These people gathered outside the French embassy in the Argentine capital, Buenos Aires. 
 
 Image copyright AFP 
 
 Several hundred people gathered in Washington DC outside the Newseum, dedicated to journalism. 
 
 Image copyright EPA 
 
 Other vigils were held in cities including Vienna, above, Madrid, Berlin and Brussels. Police have launched a huge manhunt following the deadly attack in Paris.
– "Je Suis Charlie," read signs at silent vigils around the world as thousands of people gathered to express their horror and outrage at the terrorist attack on Paris satirical newspaper Charlie Hebdo. Around 35,000 people gathered in Paris' Place de la Republique, with many leaving candles and piles of pens at memorials to pay tribute to the 12 dead journalists, cartoonists, and police officers, the BBC reports. "These killers tried to kill not only people but also the idea of peace and debate," a Muslim schoolteacher carrying one of the newspaper's controversial cartoons at the Paris vigil told the Independent. "I won't let them do that and everyone in France won't let them do that. They had no right to use the name of Allah. Mohammed would be turning in his grave. Tonight we are all Charlie." Across France, the number of people at vigils ran into the hundreds of thousands, with vigils also taking place across Europe and worldwide. In New York City, where security has been stepped up at buildings such as the French consulate, a crowd gathered in Union Square sang the French national anthem and held pictures of the victims, reports CBS. There has also been a huge outpouring of support online, with hashtags like #IamCharlie trending, and social media users sharing images like a picture of a machine gun with the slogan "This is not a religion," the AP reports.