How to get a conversation going with a girl I don't know?

[★ D11★]

I have a thing for this girl in my high school, at the end of June she followed me on twitter and I followed her back. For an entire year I have only seen her in the hallway... Over the summer I attempted to talk to her for a bit over Facebook by accidentally sending her a message, I got to know her a bit and she told me a bit about her and we chatted a bit about school and about her country and mine ( She is from Colombia, I am from Brazil). But that ended there. The new school year started and I was hoping I would have a class with her. It didn't happen. But I still see her around in the hallway and I have the same lunch hour that she has. I have noticed that always when I pass by her in the hallway she quickly glances and looks away, I end up doing the same thing. I am not the type of person that goes talking like crazy with anyone, I really feel like approaching her during lunch or when she is in the hallway. But o seem like that guy that is afraid to talk to her in person. I am a bit shy and I have noticed by the most of the time she is around her friends and I don't want to give an akward impression about me. What suggestion can any of you give me? Should I attempt to talk to her again on facebook? Some friends told me to do that, but the conversation I had with her on facebook was brief, and I don't want tway she looks when I look that she is a bit as well... I don't know if she thinks I am attractive or has a thing for me like I have for her, but I want to give it a shot... Help me out please
* Sorry, I typed it too fast... There are some errors. I said I dont want to seem like a guy that is afraid to talk to her in person. And the sentence the end when'''' I say and i dont tway... as well'''' is just messed up ignore that one