All you have to do is write up a small review of the game, on any forum you play on, make it interesting (leave out needless terms that might make people not want to play such as 'text based game' or whatever). If you're known on the forums, this is way easier, bump the thread, write interesting things, write interesting things in the bumps.
Personally I don't really share the belief that fb is the way to go, rather gamer-gamer word of mouth works waaaaay faster and better. Look at Barca's first rise in active nobles if you doubt what I am saying (guilty).
Pretty much any gaming community could work, but things that are more similar, like Paradox games (post on all those forums), Total War games etc...
Don't post like you're begging.