How to get her to like me?

Theres this girl in my school that i like. During school whenever we passed each other in the hallways we would say hey and even like give high fives to each other. One day during finals, she came behind me and poked my back to say hello. I like her and im not sure if she likes me. I tried to talk to her on facebook like 5 times. She ignored me like 1 time when i said hi and i am always the first one who says hi. It's getting very annnoying because during the conversation she will just not answer after like 30 min she will just ignore or just leave. Thats why i feel she doesnt like me. However she did like my pro pic in facebook. And im volunteering over the summer. she is supposively doing it at the same as me at the same place but i havent seen her wen i went to voulenteer. Does she have any interest in me and if not how do i get her to like me?