Theres this girl that teases me but I'm not really sure what to do...?

When we first met we were both pretty messed up at a party and ended up kissing and then whenever we're at parties together, there are some where she just comes up to me and sits on my lap and teases me but then theres other parties where we barely even talk. I know that I'm the guy and that I should initiate everything but idk what to do. I'm more if a shy guy and she's really popular. I havn't really texted her that much so idk what she thinks of me. My friends say she's just teasing me and won't give me any. But her friends tell me that they hate how easy she is. I think I'd believe her friends cuz they know her better so i think that I just need to make a move and I can get some, what do you guys think? I'm not really trying to make her my girlfriend, just a hook up. what would you guys do to make the move next time she teases me. Should I tease her back? How?