I agree about the anonymous tip thing.

And Julie is correct - not all parents are blind. Most kids at that age are apt to sneak at least just a little. It's part of finding their wings. But it sounds like these teens are doing things that have the potential to have painful long-term consequences. If my daughter were extremely intoxicated and spending the night with a house full of boys and lying to me about where she was... that's obviously something she needs parented through. The potential for some sort of group sexual encounter or alcohol poisoning is high, and to me, those have the potential to scar her for life if not kill her.

I think the question isn't *if* the parents need to know, it's how the OP can play informant without creating a situation where her own child ceases to be forthcoming with her.

This is exactly the sort of situation where parents NEED to be brought in so they can PARENT.