Bebo, Michael and Xochi Birch

Weekend Web 2.0 Special: Bebo
Michael and Xochi Birch, founders of Bebo Photograph: Patrick Fraser

Not long ago, a 17-year-old girl from Dorset vented her frustration at the tyrannical pettiness of her schoolteachers, as 17-year-olds everywhere have done since the beginning of time. '"Take your nose ring out"? fuck off biatch. im in 6th form. i dont need to comply with your rules,' she wrote, a rebel in punctuation as much as in piercings. There wasn't much to render her thoughts culturally significant, except this: instead of being confined to a diary, hidden in a bedroom, they were published - and selected as a pick of the day - on Bebo, the fastest-growing social networking site in the world.

Michael and Xochi Birch, who founded Bebo a year ago, met in a pub in London, where Michael lived and where Californian Xochi was studying.Their marriage has endured the rollercoaster ride of three internet startups, which either shows they're perfectly matched, or that they've spent too much time staring at computer screens to realise they aren't.

Bebo, like MySpace, provides its more than 23m users with a kind of prosthetic personality extension: a profile page where they can post diary entries, photographs, music, homemade video and answers to questionnaires - about their favourite things, or about what scares them or makes them most happy. Crucially, these profiles are interlinked. Beboers can leave comments on other pages, send private messages and set quizzes for each other. They can limit access to selected friends or publicise their pages to the world. The Birches are particularly proud of a feature they call ffART, for 'free-form art', which allows users to draw pictures on each others' pages (such as a heart and 'Luv u!' written in pink letters).

'We often think about social networking as the next generation of email,' says Michael, who is 36. Email 'hasn't really changed since the day it was invented.' It provides a single channel of communication: in text. 'Social networking provides a community, where you can list all your friends and find out about them, see their photos and videos, and communicate with them ... '

The average Beboer tends to speak in text-message language, may rave about tattoos or Avril Lavigne, and generally disregards the topics of Beethoven or constitutional reform. The age profile is younger than that of MySpace or Friendster. This wasn't planned: the Birches spread the word to about 100 people and waited to see what would happen.

Growth is unpredictable: while Bebo has done well in the UK and is catching on in the US, in Ireland it is the second-most visited website after Google. For now, the Birches still own the firm, paying themselves 'below average' salaries, and reportedly resisting $100m offers to sell.

The community's youthfulness has brought controversy for two reasons: the perceived risk from child predators and cyber-bullying, in which people set up user pages to ridicule a classmate. Michael says they have 18 people working around the clock to answer any queries about misuse of the system. If you use Bebo to bully, Xochi says sternly, 'your account will be cancelled'.

With two young children of their own, the Birches, who now live in San Francisco, find themselves on call for millions of Beboers as well. 'We get people contacting us saying, "They're mean to me at school ..." I'm, like, "OK, I'm really sorry, but speak to your parents and teachers and try to resolve it."'

They smile ruefully. Being the benign dictators of community bigger than the population of Australia does have its downsides.

What is Web 2.0?

People are always asking us why we're Web 2.0. I say, well, describe Web 2.0 and I'll try to answer that ... I looked on Wikipedia to find out what the definition [was] ... social networking is listed. Therefore we are Web 2.0. Broadband has allowed people to live online a lot more.

What is your big idea?

The next logical step after email. Email hasn't changed since the day it was invented ... all you know about the person who sent it is their email address - you can't click through and delve deeper and connect in other ways. Social networking fills the gap.

What is the next big thing online?

Mobile devices that allow you to take the internet everywhere you go. The interesting thing that's just starting to happen now is the concept where the phone knows where you are. It knows where your friends are ... So you may go out to town for a drink for the evening, and it'll say that two bars down the road is your best mate. And you text them and say, let's meet up in the pub in between.