British Government is urged to check on websites like Facebook and MySpace that spread wrong messages on thinning and encourages fasting in teenagers.
Medical experts are afraid that the growing numbers of teenagers in Britain are being 'sucked' into a culture dominated by websites that promote anorexia and bulimia as a 'lifestyle choice'.
Although Internet providers can shut down the sites, new ones appear as quickly in their place.
Dr Ty Glover, consultant psychiatrist on the Eating Disorders Unit at Cheadle Royal Hospital, said it had proven difficult to shut down pro-ana websites, but the situation was slightly different for sites such as Facebook.
"Social networking sites can censor their material and we expect them to act responsibly," the Telegraph quoted him, as saying.
"We are horrified at the content of these sites and the tips they give on how to be thin.
"People with eating disorders are extremely vulnerable and often have very low self esteem, so pro-ana and pro-mia sites can be very damaging as they are sending out the wrong advice," he added.
Forty British MPs have signed a motion calling for a Government campaign about the dangers of the sites. They say legislating in the area is difficult, because blocking "pro anorexia" sites from search engines would also be likely to prevent eating disorder victims from finding genuine support groups.
Experts say social networks like Facebook should act far more responsibly, and immediately remove such groups from their sites.