Is Overflow an appropriate place to solicit developer help in open source project? if not, can you recommend me resource to do so?
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There is and Open Source Advertising program just for that purpose.
As others have said soliciting help is not an encouraged practice (not in comments or posts), you are welcome to ask specific questions regarding issues that pop up during development.
Also, you can inform users of your project on your profile page, pretty much anything goes there.
As for the how to get help part, I run a fairly successful open source project with 20-30k downloads a month and a very active community. I find it very hard to recruit developers, its just the name of the game. Make it easy for devs to join your project (have plenty of documentation) and welcome contributions (In my opinion having a distributed version control system play a very important part, cause it makes it much easier for people to contribute)