You can search on LinkedIn, Quora, then connect with the developer and then talk and find out if the developer has got some Github links, app store links, for you to evaluate his/her work.
Find out their expertise, and then when you finally trust the developer, ask the developer to sign an NDA and then share your idea, and finally, when the developer starts showing his/her interest by contributing to the idea, you know, you have done the right choice.
You can search on LinkedIn, Quora, then connect with the developer and then talk and find out if the developer has got some Github links, app store links, for you to evaluate his/her work.
Find out their expertise, and then when you finally trust the developer, ask the developer to sign an NDA and then share your idea, and finally, when the developer starts showing his/her interest by contributing to the idea, you know, you have done the right choice.