Should I message him?

I've liked this guy I work with for a while now, we've never spoken before because we work in a big call centre and haven't really had the chance to chat, but always made lots of eye contact when we saw each other. Anyway I found out today that he's left the company and I'm a bit gutted, would it be weird if I messaged him on Facebook or sent him a friend request if we've never spoken before, and should I come straight out and ask him out or just say hi?
Should I message him?
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