For preposition of places, should Facebook, an internet space, be used as in or on? E.g.
Find us in Facebook.
I usually hear "Find us on Facebook." It's the shortened version of "Find us on the internet site called Facebook". And since site (whether internet or not) is used with on, Facebook also is used with on. Same goes for the page (also does not matter, internet page or a book page) by the way.