Adverts show how the apps can be used to alter body parts, including making waists slimmer and adding muscles.
Eating disorder charities have said technology firms should consider the impact on vulnerable people.
The platforms said the apps did not break advertising guidance, but TikTok added it does reviews its policies.
It said it is “continually looking to enhance” its framework to “support a body-positive environment”.
The social media platform, popular with teenagers, banned adverts for fasting apps and weight loss supplements last year.