easy. talk to them.
if that doesn't work, take it away from them.
"but they'll just do it at their friends house" cool, you're grounded.
"now they just do it at school." cool, I'll buy ad space on the platform and target the school with wanted posters with their picture on it. any student that can send me picture proof of them using the platform will get a reward. maybe even give away more of their stuff. know anybody who wants an Xbox?
"now your kid hates you." cool, I'm their dad not their buddy. it's my job to make sure they are protected and capable of understanding the risks of their actions. if they want to rebel they need to understand there are repercussions.