is the final result going to be some sort of product or service that you would be "selling" to people? if so then go to services board and post what skills you are looking for and hire developers to develop what you want. find an escrow and put their payments with that escrow until they finish the job and the escrow releases their payment.
The difficulty here lies in how to define the escrow? Is it a guarantee to deliver the code? How to verify that it is safe? Without any backdoors? How to develop the project in the future?.
I do not think that relying on anonymous people to build an idea or develop a site/app will be feasible in the long term.
The idea of an open-source project is the best solution but I think you need to forget the business segment.
Ideas do not bring money, you need to develop your skills more than that.