I have found that job posting are enough. Of course, you should try to tap your network whenever you can, but in practice that will mean a much smaller pool of people who are both qualified and looking for a new position.

Also do you find different job postings work better for different networks? Github vs SO vs Glassdoor.

Which networks have you found most effective for finding good engineers?

I love StackOverflow careers. They are expensive, but draw a quality crowd.