How are girls actually using social media? My impression is that the problem isn't so much obsessively posting as merely scrolling through content, thus a social media account for the purpose of infinite-scrolling isn't necessarily going to appear to be for someone underage or even be surfaced to anyone who would even care enough to report it.
Obsessively posting is really common. Kids’ friends post all the time, especially including Snapchat. It seems bizarre to me as there may be 10-20 posts per day per kid.