Britain's teenagers have a secret. The money spent by media companies buying up well-known internet chatrooms such as Friends Reunited and MySpace has missed the target. New figures show that the busiest community website is the unheralded Faceparty.

Teenagers are so obsessed with the site that last year it saw more traffic than Yahoo's email service, Tesco's website and Amazon. Only eBay, Google and Hotmail are viewed more often in Britain.

The site allows its 6 million members to send each other messages. Members have their own mini-sites with pictures of themselves and details of their tastes. They can browse other members' sites and start conversations with thousands of people they have never met.

'I check my messages every single day,' explained 16-year-old James Hardman from Leeds. 'All my mates do it. We want to find some nice lasses and just text and email each other. We're meeting a couple of them in the school holidays.'

James is one of the rare members brave enough to put his phone number on the site, but says he has only been bothered by 'weirdos' once or twice. He is more coy about the 'adult section' of his site, where members can put up naked pictures of themselves and choose who gets to see them. 'My pictures are quite rude but I haven't let anyone see them yet. I'd be very careful about that.'

The popularity of the site has raised concerns: some parents are worried about inappropriate banter on the site, and the possibility that some 'young people' are adults posing as teenagers.

Members are encouraged to sign up for special privileges: for £24.95 a year they are no longer restricted to sending five messages a day, and for an additional £38.95 over-18s can buy the right to see the site's adult content.

Rupert Murdoch spent £334m to buy the similar site MySpace last year, but it seems new media cannot be controlled as easily as the traditional press. 'Cat', 19, says: 'I definitely prefer Faceparty to MySpace. MySpace is all corporate now.'

The technology magazine .net recently proclaimed Faceparty to be 'best community site'. Its editor, Lisa Jones, explains: 'It's really grown under the radar. Since Murdoch bought MySpace, everyone's heard of it. But Faceparty has got this underground appeal.'

Gemma, 17, joined after a friend's recommendation. 'I only checked it out because one of my friends made me and now I'm hooked. It's the best way to kill time at college.' The director of Faceparty, David Bamforth, says: 'The grown-ups know all about MySpace, but very little about us. Their kids get home from school and spend hours on it. We try really hard to keep out of the press.'

The site offers a rare glimpse behind the sullen exterior of Britain's teenagers. Laura, 16, from Nottingham, is happy to share her philosophical thoughts: 'I live life 2 the full, REMEMBA U NEVER MISS A GD THING TILL IT LEAVES YAH.' Members are also asked a series of questions. Most struggle to name a favourite author, with pop stars scoring highly. Laura's effort is typical: 'Jordans Autobiography is wkd bt i dnt really read.'

Nick Barham, author of Disconnected: Why Our Kids Are Turning Their Back On Everything We Thought We Knew, says: 'Online communities are all about sociability. It's just a different kind of sociability. You decide how the world will see you - your best-looking, or stupidest, photo. Your favourite phrases, not your embarrassing silences.'