I started back in the day with MySpace, then Craigslist. Over time, I built up word of mouth referrals and also did freelance work for a bunch of agencies/companies for a period of time, sometimes finding them through (crappy) recruiters.

If I were starting today, I'd use matchist (matchist.com, the new startup I'm building). Our goal is to become a trusted referral source in your inner circle.