My best friend is a complete dimwit and shes at a sleazy guys house for the night. im worried?

She's just like a stereotypical blonde, but slightly smarter... don't get me wrong, I accept her for who she is and I love her to bits (like a sister) but shes completely oblivious to everything. She's away for a dance workshop And this guy she's staying with is a drug addict and is not trustworthy. Her parents let her...she's only 16. She is afraid of sex and hates drugs, even caffeine... she thinks this guy is totally cool because "he told her he was trustworthy". Therefore she won't listen to me. He isn't fake, we've both met him but he's 19 and he WILL do stuff and take advantage of her. What do I do? I'm on here cause I have no other options atm.