A study by the University of Exeter shows how Twitter and Instagram accounts are celebrating extreme thinness, with users invited to say they "like" images.
‘Anorexia nervosa occurs mostly in those individuals striving for success in industries that demand a slim body image such as modelling and dancing. There is also a higher prevalence of anorexia nervosa in higher social classes.’
This so-called "bonespiration" content features selfies by young women of their skeletal bodies featuring protruding collar bones, hip bones and spines in a variety of poses.
Its purpose is to boast about a skeletal appearance and inspire others to achieve the same emaciated look.
There are numerous versions of the bonespiration Twitter feed, and Instagram accounts. Some platforms for posting such images are hidden within mainstream sites.
The research, led by a psychologist at the University of Exeter's Medical School, shows there are thousands of account holders. The images of protruding bones are almost exclusively posted by young women.
The study analysed 730 images posted. It found 26 percent of images showed hip bones, 23 percent showed jutting ribs, and 22 percent showed protruding collarbones. 6 percent of photographs analysed depicted the spine.
Academics fear that social media has replaced the pro-anorexia ("pro-ana") websites, and are becoming an easy to access way of encouraging eating disorders, such as anorexia.
The sites flash up a question asking if they need help, but researchers say the platforms raise question about whether tougher regulation is required.
They fear efforts to ban the images would lead to others with different hashtags appearing within days.
More mainstream twitter accounts such as 'thinspiration', which features photos of thin celebrities, also depict young people with protruding ribs collar bones and spines, the research found.
The research found a small sub group of people posting skeletal images with the hashtag 'fitspiration', which is dedicated to inspiring supposedly healthy bodies.
The researchers say the sites are being used to promote extremely unhealthy body types and are increasing pressure on teenage girls to try to become extremely thin, while contributing to a distorted view of their own body.
Ms Catherine Talbot, a psychologist and PhD researcher at the University of Exeter Medical School and lead author of the paper, said the photos were a form of "social contagion" and inspiring young people to engage with risky practices.
"Anorexia and extreme weight loss is a serious social and medical problem. To tackle this social contagion we need to be aware of the social media platforms being used by young people - mainly girls and young women - which is encouraging extreme weight loss. This behaviour could seriously damage their psychological and physical health," she said. "Teenagers need to be taught about positive body image in schools and we need to build resilience."