For licensed electricians I've had good success from advertising in our area's largest newspaper, the Boston Globe. Many responses. I tried 4-5 smaller, more local papers with poor results. Ads are expensive, but at least you get what you pay for. When I thought about it, if I were looking for a job, the Globe is where I'd look too.
I've had a lot of success hiring apprentices from other trades. I have 3 excellent apprentices who formerly worked for a HVAC company. Good people, excellent mechanical skills, just needed to learn electrical. Working under a good licensed electrician, they progressed extremely quickly, and one has since become licensed. One contacted me, and the others followed his footsteps a year later.