It depends, are you looking to outsource (you will never have an in person meeting with him) or a local Developer.
For Local developers I recommend Meetups related to the kind of app you want to develop (if is a native mobile app don't look in the web meetups and so on), users groups (some has been converted to Meetups, but still user groups), hackathons (a bit difficult since most of them you have to participate but I have found two great developers on those events), asking around to friends and colleagues.
For outsourcing, well I have used Odesk and Elance, but I have to do a lot of research in order to be happy with the person, so now I rely on recommendations from friends and I work much harder Managing the Project.
A recommendation be clear on what you want to develop, divide in task and milestones, take one or couple tasks that you need to have done to get started but are minimum risk or easy to refactor, and assign that to the developer you select, see how you feel with his interaction and the results, if you like it then go higher and higher.
Do not do what I have seen so many times where the person hire a developer is not clear on what they want can't prepare a project plan on what they want and much less identify tasks or areas to focus give the rough idea to a Developer to work in the entire thing and after a while they see what the developer has done and is not what you had in mind or is totally unreliable or is not even close to be done, you only can do that if you have worked with that developer before and you have complete trust, if not be ready to be frustrated and not happy (and believe me the developer will be frustrated as well and likely will not work with you again or will charge you a high amount). I am telling you because has happened to me in both sides, hiring the developer or being the developer.
Don't do the joke of hire a developer and tell him I want you to do me a website a website that makes me millions and you give him no more information, believe me if the developer knew how to do a website that can produce millions he will be working on it and not for you.