Halp - dating advice needed

Went out last night and in a beer garden, while waiting for the toilet got chatting to a guy. Pretty spontaneous casual chat and we bumped into each other a couple mire times that night. Turns out he knew the friend I was out with that night and offered to buy us both a drink. I added him on FB and he added back.

Should I message this guy today? Or just leave it?

If message, what do I say?!? 😬