How to tell when a girl is into you on facebook.?

I didn't really do a whole bunch of dating, I've had intoxicated sex at parties a couple times, but thats it. so I'm kind of new to this. How can you tell when a girl is into you with her comments, because it IS in fact a lot different when you're around people in person verses the internet. I'm talking about people I know in real life who are on facebook. Not e-people.