That seems little different from the opposite end of the spectrum where anorexics form "support groups" to encourage each other to be anorexic. I don't know if there is a right way to deal with it. Maybe you could ban those groups from online platforms, but that won't stop them from doing it "in real life." These people probably need mental healthcare, but there's no humane system in place to force treatment on them (and forced treatment probably wouldn't be effective anyway.)