check with your local BBB. Good contractors are still busy and they do not need to waste resources posting for ads on line. Most all of these are agents that will send dozens of unqualified contractors.
I've used Craigslist and Angieslist, both with mixed results. I've gotten great deals on good stuff from the internet, but I think the best way to get a good sub is to talk to people that have used their services before. I am a framing sub and I've gotten lots of work from people asking for referrals from builders and realtors. I hired a "plumber" from Craigslist and he was a joke, a scammer, a liar, etc... Do serious research on references and qualifications before you agree to ANYthing.