This is a tough question. I'd say it depends on what kind of designer you need! I'm a product designer in SF, and I work with many amazing designers. I can say

This is a tough question. I'd say it depends on what kind of designer you need! I'm a product designer in SF, and I work with many amazing designers. I can say that the vast majority of us are not publishing on Dribbble, Behance, etc. I would recommend posting jobs on Dribbble, however. That's probably the first place I would go if I were looking for a new gig. Designer News and Angel List are popular. Also Stack Overflow and GitHub for the more technically-oriented designers. Lastly, I'd recommend word-of-mouth on Twitter. The design community there is pretty robust.