First thing I would say is read The Lean Startup by Eric Ries. He goes through the process of validating an idea very clearly in the book. Bottom line, you should find advertisers and validate that they are willing to pay for what you want to build, then you need to find your users and make sure that it is a system of value to them.

There's a whole host of product development firms and employees that you could hire, but ultimately, it doesn't make sense to build something until you've got your users saying they'll use the platform and your customers saying they'll pay you (preferably in writing).