Snitching won’t help. Unless you can bring the kids back, just ignore it. They’re either gone anyway or they’ll outgrow their teenage rebellion.
I recently stumbled upon a double FB account belonging to a good bochur here whom I know very well – and another FB account belonging to a girl who is not frum but is in the frum school here because her parents are returnees from EY and want her in a Jewish environment (knowing probably that she’d end up in real trouble otherwise).
The girl’s photos on this account are not acceptable and clearly show she has no shaychus to Yiddishkeit. I was shocked but not surprised at the girl’s profile but totally surprised that the bochur had a second account for an online relationship with her.
I just blocked the accounts because they’re just kids fooling around and all I would accomplish if I reported it to the boy’s rosh yeshiva is that the boy would go OTD. Reporting the girl is not my job and this is a kiruv community so they’d never do anything so long as she isn’t breaking the rules in school itself.