Nude pictures of under- age girls on website.
A teenager from North Wales was among those pictured on the Faceparty site.
The girl,calling herself Linda,described herself as a lesbian and gave her age as 23 but later said: ``I am 15 really.''
Her entry, before its deletion, included five nude photographs.
Teenagers appear to be using the web site to offer pornographic shots in exchange for mobile phone top-ups and other gifts.
The website, which is one of the UK's largest, is designed to allow its 2.4mmembers to swap messages and meet new people. Children apparently as young as 13 are using the site, which experts fear could be used by paedophiles to hunt potential targets.
Faceparty banned the apparently under-age members and removed their photos within 90 minutes of being alerted, and a spokesman said programmers were attempting to work out new ways of keeping children off the site. The statement also pointed out that all members signed up to terms and conditions which warn they should not download obscene material,including ``any naked photographs where the model is or appears to be under the age of 18''.
The web site does not allow any members to list their ages as under 16.
A spokesman for the police's National Hi-Tech Crime Unit said it was ``physically impossible'' for web sites with such large databases to monitor all the information.
Officers would now liaise with Faceparty to see the material was removed and measures put in place to prevent more child porn being posted on the site,he said.