Is it weird to randomly message a girl?

[Charlie]

Basically, there is this girl that really like from my church. I usually see her once or twice a week and we talk a bit - not lots though. I have never chatted to her on Facebook before however I really want to, to be honest. She liked my latest status update (which only got seven likes ). Would it be weird for me to randomly message her and, if not, what should I say?
Thankyou in advance.

Extra information:
I think she likes me a bit because she looks at me differently to other girls, we both have the same favourite animal, she knows I love guitar and she plays flute, I'm a year older and I would call myself popular at school, I am, I think, a bit more at church though. I don't have her number atm , how could I get that because is it weird to ask her this late?