How do you ask out a girl you really like who you do not see very much?

Ok, So there is this girl who I've had a crush on for over a year since freshman year. I was in her math class where I first saw her but I could never get up the courage to really say anything to her. Now I am not in any of her classes so I can't really try to talk to her. She is incredibly beautiful, nice and very outgoing and she has not had a boyfriend since freshman year, but I have heard she is looking for the right guy. I am friends with her on facebook and her birthday is coming up so I am gonna write on her wall so she at least notices me. I don't know if I should talk to her on there because it would probably be awkward because I have not talked to her much in person. I also need something to talk about like an ice breaker that I can use in person. There is a big dance coming up early next month which some of my friends think I should tell her how I really feel. They think she would really like it. One of my friends is good friends with some of her guy friends (who I am sorta friends with) and he thinks they will back me up if I tell her how I feel. but I feel like if I tell her how i feel she will tell some of her friends who might make it a big deal and tell everyone and it would just be bad. or she will humor me and almost be doing me a favor which i would not want. I feel like I should just talk to her instead of doing that but like I said I need an ice breaker or something like that and since I'm not in any of her classes it would be hard. I've been told by many people that I am really funny and I am able to get get people laughing which would probably help. I just want to know what someone would do in my situation. HELP!!