WASHINGTON (CNN)  -- The family of a retired FBI agent who was reported missing in Iran two years ago said Monday that they remain hopeful for his return.



Photos from Robert Levinson's family show him in 2006, left, and as he might look today.



Monday marks the second anniversary of the disappearance of Robert Levinson, a father of seven children and grandfather of two.



"After two years of constantly praying for his return, we continue to anxiously await word of his whereabouts," said Christine Levinson, the missing man's wife, in a statement.



"Two years [have passed] since our seven children and I last heard his voice, saw his warm, loving smile, and since we last hugged him hello or kissed him goodbye," she said.



Tuesday will be Levinson's 61st birthday.



Levinson disappeared during a business trip to Iran's Kish Island in 2007. Iranian authorities have said repeatedly that they do not know what might have happened to him, but the claim is widely doubted in the United States.



"Since that day our family has been living a nightmare," Christine Levinson said. "This has brought so much darkness to our lives."



Christine Levinson released a computer-enhanced photograph showing what the family thinks Bob Levinson may look like today.



The State Department has consistently denied Levinson was working for the U.S. government and has unsuccessfully pressed Tehran for information about his whereabouts.



"We reiterate our commitment to determining Mr. Levinson's welfare and whereabouts, and reuniting him with his family," acting State Department spokesman Robert Wood said in a statement on Sunday.



Congressional reaction in Levinson's home state of Florida has been more pointed.



"On several diplomatic occasions when Bob Levinson's name has been brought up to Iranian officials, the standard answer is, 'We don't know anything about that.' But the next thing out of the Iranian officials' mouths are to discuss the matter of the Iranians held by the Americans in Irbil, Iraq," Sen. Bill Nelson, D-Florida, told reporters last month.



"You can draw your own conclusions," he said.



U.S. troops arrested five Iranians accused of being members of an elite Iranian military unit during a January 2007 raid in the Iraqi city of Irbil. The Iranians were accused of supporting Shiite militias in Iraq, but Iran said they were diplomats and accused the United States of violating international law by raiding a consulate.



Nelson and Rep. Robert Wexler, D-Florida, have said they plan to introduce legislation in their respective chambers calling on Iran to cooperate with the United States and come up with information about Levinson.



Levinson had been working as a private investigator in Dubai. He was last heard from on March 8, 2007, when he checked into a Kish Island hotel and then checked out to return to the United States the following day.



Wexler has said Levinson never arrived at the airport for his flight home.



In December 2007, Levinson's wife and other relatives traveled to Iran and met with officials. Christine Levinson has said the Iranian government was polite and guaranteed her family's security on their trip, but provided no details regarding her husband's whereabouts.



"In the past two years, our family's grief has grown to despair," Christine Levinson said.



The State Department is asking anyone with information about the case to contact the department or the Levinson family via their Web site, www.helpboblevinson.com.



CNN'S Jill Dougherty contributed to this report.
Whose family is "constantly praying for his return," wife says? Where is the Iranian claim doubted? What is the name of the family? What are Robert Levinson's family praying for? Where did Levinson disappear from? Who says they have no knowledge?
Robert Levinson's in the United Levinson, his return, a business trip to Iran's Kish Island Iranian authorities
question: Whose family is "constantly praying for his return," wife says?, answer: Robert Levinson's | question: Where is the Iranian claim doubted?, answer: in the United | question: What is the name of the family?, answer: Levinson, | question: What are Robert Levinson's family praying for?, answer: his return, | question: Where did Levinson disappear from?, answer: a business trip to Iran's Kish Island | question: Who says they have no knowledge?, answer: Iranian authorities