Messaging a girl back?

So there's this girl that added me on Facebook a couple days ago and we started talking, getting to know each other and being funny and all that, my guy friends know her in real life and I don't but she's really honest and really fun to talk to online, like we would stay up and talk.. Now I don't know it's been a day since I last messaged her, should I message her again or wait it out?
Messaging a girl back?
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