Should I be worried that she didn't message me back?

[James]

I did some little flirting with her on facebook for like a week (I liked her new profile picture, we had a poke war, commenting random google images on her wall for like an hour lol, etc) and then Monday she poked me, and I poked her back, but now she hasn't poked me again since the (she's usually almost never on during the school week though, last week was weird). I wanted to ask her to hang out this weekend sometime, so then two days ago (Thursday) I saw her on and I said "hey loser" to her on chat, but she didn't reply and it turns out she didn't even see it until last night (Friday). Should I worry that she didn't message me back? I mean I wouldn't message someone back a day late if they just said "hey," so I don't think so. And should I try messaging her again tonight or should I wait a day or two longer?
Thanks
PS I know that just because I flirted a bit with her doesn't make her mine for the taking, but it just seemed weird that she abruptly stopped all contact.

[Jennifer]

wait a day then ask her if she is OK,

[L]

Come on, it's only on the net. Why you are thinking too much. It's just like a game. Today you feel good and have time for that person to poke or chat with, tomorrow is another day and maybe you have other things on your mind to do other than messaging, texting or whatever. Keep your cool. there are so many ladies out there.

[Noelle]

You are assuming. What if her house burned down her computer died, family problems. You don't know. Be patient and if she does not respond contact here a different way and ask did I do some thing. But what ever you do don't make it sound like your accusing her or she will get defensive and that will be worse. Be opened minded.

[Aashnaa.]

girls can be hormonal, weird, confusing, and we will overthink EVERYTHING.
But she seems like she really likes you, so don't give up hope, hun!
She may have other stuff going on so she can't reply, but don't worry, it won't necessarily be anything YOU'VE done!
Don't give up on her though, message her soon to let her know you're still there for her and you still care, but don't overdo it if you get what I mean?
best of luck, let me know how it goes and if you have any other questions! (: <3