How to tell a girl that does not know I'm in love with her?

[Roberto]

I see her every day at school, she demonstrates to be interested in me, but she is always accompanied and therefore I can not approach her.
I've tried talking to her for facebook, but she does not use facebook much and usually only go there at night, there are days that neither will, I sent a message saying "hi", but she has not seen her (I know this because did not show the "seen") and I'm hoping she answer me to start a conversation, but it's weird every day to see her and could not do anything. She usually looks into my eyes when I pass by it.
I love her very much and so do not want to blow it, I'm not holding this more heart ache.
Someone I can advise them anything?