How do I start a convo with her without being creepy or weird?

[Micheal Martinez]

There's this girl that before I even hanged out with her friends and met them, she would look at me and smile and other times just look and I could feel sometimes like she would check me out, I'm 5'11, buff, I'm really nice and cute (according to girl compliments) and after I even became close with her friends she still would look a me like "damn your fine) btw she's a freshman and she looks 16 or 15 but she looks older than her age, I'm a junior 18, but we obviously aren't gonna go out, the last time 2 weeks ago we were all there mutual friends of hers and her name starts with a K and my crush Is N, so like K came and stood super close to the left of me and my left hand was so close to her a** so I backed up a bit, and ever since I guess K found out I have a crush on N cuz they both hang out and Now K looks at me all mad not literally but I can tell, and I was thinking of Adding K on Facebook, so like I send her a request and accepts me 5 or 7 minutes later, and I was thinking is it better to talk to her in person or through Facebook inbox? It's because in school I don't have lunch with her although I use to, I only see her in the halls but its rare when I do. What's a good idea to talk about her or to start a Convo with her? Like I said I've always hanged with mutual friends of hers and she' was always there so like she knows who I am but we've never talked before, I was thinking of showing her these cool dance party song I liked Bc I remember she would always be listening to music and going on her trip dancing and I was thinking of showing her the song but how can I start a convo about it on Facebook or in person??