An investigation by a BBC Wales programme has revealed sinister online groups are threatening the lives of youngsters with eating disorders.
Kirsty Ball has suffered from anorexia for seven years
BBC Wales Week In Week Out programme reveal that anorexia sufferers are being sent messages and images urging them to continue starving.
Youngsters are encouraged to celebrate anorexia as a lifestyle, not a disease.
There are thought to be hundreds of "pro-ana" websites glamorise thinness and give tips on deceiving doctors.
The sites are being blamed for undermining the recovery attempts of extremely vulnerable sufferers.
Kirsty Ball, from Chepstow, south Wales, is 18 but weighs just over five stone. She is convinced she should continue losing weight.
She has suffered from anorexia nervosa for almost seven years. A severe mental illness, it has devastating physical symptoms.
Kirsty has an illogical compulsion to starve herself and to vomit what little she does eat.
"I get scared of not being able to count every rib or feel my hips protruding," she said. "You lose all perception of what a normal body is."
Despite the help of doctors and psychiatrists, Kirsty is still in the grip of the disease.
After years of trying and failing to recover, she turned to the internet for support.
She found an online community of fellow sufferers who shared their harrowing experiences in chat rooms.
"It was a relief that I wasn't alone - that there were other people that thought like me," she explained.
But, like so many others who set out in search of comfort, Kirsty quickly fell prey to "pro-ana" chat rooms and websites.
She soon came to depend on them and describes in BBC Wales' Week In Week Out programme how she would turn to faceless strangers online for encouragement whenever she wanted to lose more weight.
Disturbing photographs and messages from other emaciated sufferers only served to spur her on.
"You can see a picture of someone else that's died from something that you are doing, and it's not enough to stop you," she said.
Eating disorders affect up to 60,000 people in Wales and experts are warning that many doctors are not spotting the symptoms early enough.
The Eating Disorders Association is highlighting its concerns in a week-long campaign.
Week in Week Out examines the devastating impact the "pro-ana" movement is having via the internet.
The programme tracks down a 16-year-old anorexic girl from rural Wales whose harrowing online diary reveals her suffering.
She writes: "I hate the way it makes me feel, all dirty. I hate it when I can feel it wriggling about inside me like a parasite destroying me."
Like Kirsty, she searched the net for support and understanding but fell under the influence of chat rooms - where strangers encouraged her to become dangerously underweight.
Week In Week Out, BBC One Wales, 2235 GMT on Tuesday, and again on BBC 2W at 2100 GMT on Wednesday.