How do I reconnect a relationship with this girl?

[Tony]

I'm a senior in highschool now, and I used to talk to this girl all the time when I was a sophmore. We were really good friends. I never had the courage to ask her for her number, I only have her added on facebook. We used to always say hi in the hallways, but now we just walk by and act like we don't know each other. How should I confront her through facebook if I don't have any classes with her? Should I just straight away ask for her number or what?..
What should I do if she doesn't reply through facebook. I see her in the hallway, but we act as if we don't know each other.

[Angie]

start with conversation first then go with asking her out or phone number

edit: start getting close to her group of friends or when u see her alone go to her..its risky for u i knw... but life is all about risks

[physicshelp]

message her on facebook saying something like "Hey! i havent talked to you in a while how have you been" and then just converse and say at some point i have to go you can text me if you want