Sex at 15

DeVona
No this post is not about me, but I just found out my 15 yr old sister is having sex. Not only that getting fingered as well...I had her phone and the guy she's talking to is trying to record them having sex. I took her phone but that doesn't mean she'll stop. I've tried talking to her as well but how do I get her to understanding sleeping around isn't cute? She has her whole life why sleep with these guys who mean nothing a couple of months later?