Build up your friends list. Go through this thread, add people you recognize. Add people with a lot of posts in the official L4D thread. Add people you play with. Add me (Steam name Oreoleo)! There are ALWAYS people playing. Shit, it's 9:30 on a Saturday morning and there's still 4 people on my friends list playing right now. And obviously during more normal hours there will be more playing and if there aren't, people are usually willing to join if you send them a game invite. It's pretty easy to get a game going when all's said and done, Valve has a pretty loyal following. And it doesn't hurt that the game is totally sweet