How to talk to a girl you don't know?

[Coltrane]

I like this girl and I've seen this girl around school. I don't have any classes with her. I wanna talk to her but she's always with her friends. So how do I talk to her? And would it be too creepy when I introduce myself to ask her for her number since I only see her like every other day or should I just wait till I know her better and then get it?
I'm a senior and she is too. (Kinda disappointed that I need help and I'm a senior lol.)

[Ally]

aw, try to add her on FB, follow her on instagram or twitter and make a convo, as she talks to you make the convo long and stuff and when she finally recognizes you, say hi, or wave then you guys finally know each other good luck! answer mine, please?