What to say to this girl on facebook?

[Daniel]

There's this girl I find pretty attractive...She's my friends step sister, , but we've never talked. She "liked" a post my friend's mom put on her sons page that was 100% about me. I usually don't talk to random people on facebook, but I thought I'd give it a try.

So I messaged her saying what's up, she was like "do I know you" and we talked for 5 mins or so, she liked 5 of my pictures, then she never messaged me back.

Should I message her back, and if so, what should I say?
Yeah I keep posting it bc things change

[Kylie]

You keep posting this.. You could start with hi, maybe mention the thank you're friends with her step sister. Girls wont judge you on how you say hello. and most often they'll answer you. you can say whats up? if she doesnt answer you you could say "or ignore me, thats cool" or just wait for a reply. To keep the conversation rolling just ask her questions about what she likes doing or her hobbies etc, and if you have anything in common you can always talk about it. Like favorite bands, gossip etc. Believe me, talking to girls is all psychological. It's really simple and also one good tip. If the conversation is dying just say "oh sorry i have to go now" or some crap like that, it will save you the trouble of thinking. Also try and talk to her in person too.