I bumped into my ex-classmate yesterday i just said hey to her and quickly walked off as i am rushing off to a meeting, we heaven't seen each other for 4 years.
A few hours later one of my bro showed me a conversation between my ex-classmate and her best friend(who's one of my current classmate) on twitter.
My ex-classmate mentioned that "i look sooo much better and that she kinda miss me. "
Her bestfriend told her that she is gonna show what she wrote to me
and she replied "NOOO!! DON'T DO IT!! HAHA! But I felt surprised seeing him hehe"
They then went on and on about how much i had changed for the past 4 years
She then asked her bestfriend if I had a twitter account (which i don't), because she don't want me to see what they were talking about.

How do i approach her? Will she think i am creepy if i text her?(we aren't close friend and barely spoken to each other back then)
And they doesn't even know that i saw the conversation that took place between them.
What should i do?
I am able to meet my ex-classmate's bestfriend everyday as i am in the same school with her currently.
She's apparently shy, i don't want this to end up awkward between me and her.

Okay so from the sounds of it she finds you attractive and interesting. This is a good thing. She is waiting for you to make a move on her.

Since you don't have face to face contact with her everyday you may need to set up a get together with your friend who is her bestfriend. That way you will be around her and it will be a low pressure friendly situation(not a date). This will give you oppurtunity to start building rapport with her.

Don't make a twitter account just to contact her. She will pick up on this and it will make you look needy. If you make a twitter account make one just because YOU want to.

You could possible have your friend be the mediator between you two, but the only problem is she may think her bestfriend showed you her messages.

OR you could have your friend "Set it up" for you. Have her say "Hey will you know im good friends with ____(you). He asked me about you the other day. He says he wants your number so you guys can hang out/or call you sometimes."
Simple as that. From the sounds of it she should give a good response and then your in!

These are the only two approaches i see in this scenario. I think it should be pretty easy though. Dont think about it to hard though.

Good luck!