A group of top psychiatrists have warned against the pro-anorexia sites that are soaring in popularity through blogs and social networking groups.
Online members compete with others to lose weight, share tips on disguising anorexia or bulimia from family and doctors, reveal crash dieting techniques and recipes and upload images of dramatic weight loss.
"When I was really desperate I'd go on all the time, looking for tips on the latest diet and wondering what to do next," Sky News quoted recovering anorexic Emma Columbine as saying.
"And seeing photos of skinny celebrities - I just aspired to be like them," the 20-year-old added.
The Royal College of Psychiatrists' Eating Disorders Section warned against its effect on young people, saying greater awareness was required to deal with the dangers of such groups.
Susan Ringwood, from eating disorder charity BEAT, also said: "We want to increase awareness about these websites and make sure people know the dangers.
"And also to tell people that there are good positive resources out there for people with eating disorders that can help recovery, not encourage illness."