LinkedIn is an interesting tool for freelancers. I've gotten several clients from the service simply by having a filled-out profile and joining user groups for the languages and frameworks that I specialize in.

I've gotten clients such as AppDev and the Flatiron School from LinkedIn. Interestingly enough, I was never proactive with reaching out to clients. If you have a good profile showcasing your skills and you have joined enough groups, jobs start to come in. It's incremental growth, but I've found some great clients though LinkedIn.