Should I tell my friends that drugs were at a party I was at?
Why do you want to tell them that?
Because I have a strong suspicion that a girl at the party was tempted to take drugs.
You shouldn't tell your friends about illegal activity like that. It's not your place to bring things like that up.
Why not? That will help save her from falling into a trap.
It's good that you are trying to help her. You need to be careful about how you go about this whole situation.