I generally don't. I generally don't hear about a game until it's been round a while, like a decade or more. I'm a bit boring like that.
When I do find out about something new to me, it's usually been a friend who's heard of it or recently been introduced to it and wants to share. Or it's on G+ (which isn't dead, despite the rumours, and provides a real community feeling for roleplay gamers).
Yeah, short and boring answer today. Sorry.