I've only been freelancing for about 5 months, but so far I've just been referred into work from my friends on Twitter. My first job, the client approached me through my site - ever since it has been followers on Twitter who need work done themselves, or who have recommended me to whoever they know that needs a developer.

I think this has probably been helped to some extent by networking with a lot of these people in person at meetups. There's no substitute for coming across as a nice guy who is knowledgeable and enthusiastic about what he does.