Half of girls now report feeling pressure to be thinner, while one in four people say their appearance is the most important thing to them, he warned.
Writing for the Daily Telegraph, he said: “Where celebrities and the platforms which promote them exploit this vulnerability by pushing products like laxative teas, diet pills and other get-thin-quick solutions, they are taking the health of our young people in their hands and should act with far greater responsibility.
“Online platforms should stamp out accounts which exploit this vulnerability, and ban adverts for products with a known health risk.”
The leading doctor’s intervention comes after social media companies’ practices were thrust back into the spotlight over the death of teenager Molly Russell.
The 14-year-old’s family found she had viewed content on social media linked to anxiety, depression, self-harm and suicide before taking her own life in November 2017.
Her father, Ian Russell, told the BBC he had “no doubt Instagram helped kill my daughter”.
Health Secretary Matt Hancock said social media firms need to “purge” the internet of content that promotes self-harm and suicide.
Meanwhile Culture Secretary Jeremy Wright has said the Government is “considering very carefully” calls to subject companies to a legal duty of care.
And NHS England chief executive Simon Stevens has proposed the introduction of a mental health levy on social media firms.