An app that fills a very needful gap in the social space today, and I run a functional media agency that will aid fast creative product design and video advertorials for publicity
Why partner? Why not hire?
Partners will ask about how you have reduced the risks as much as possible, partners need to receive direct benefits from the partnership, and partners will want some say in how things move forward.
From your brief description it sounds like you want to run a creative agency, not a social networking app. You will not find a partner who just wants to do what you think you need. You will need an actual business plan for all aspects of the enterprise you imagine. That includes validating your idea, validating your marketing strategy, and finding the product-market fit for all aspects. It sounds to me like two distinct businesses, and that's not going to interest most people. Pick one. Let the other grow organically out of it ONLY when your core customers start asking for the expansion regularly.
There are a zillion creative agencies. Don't compete. Do the thing that's unique.
Start by making a list of each and every single assumption you have made. Then test each assumption individually to find out how far from the mark you are.
There are many people skilled in making these kinds of apps. In order to find a developer, one should be very precise about what part of total space you are trying to cover. The same developer who might be an expert at a web app for desktop computer use, might not be any good at making a mobile app. Social networking programs typically have custom apps for mobile because the browsers on mobile have technical restrictions, and use up valuable screen space. So you need first to nail down the platform range. If you end up wishing to make a cross-platform product, then you either need a team of people, or a person skilled in one of the cross-platform technologies that can with a single programming effort deliver on the various devices. I myself am working on such a cross-platform tool, and it is very challenging. When you have a strong product idea, it is best to cover as many platforms as possible, because people are not going to typically switch cellphone brands to play with your app. Some people just pick a single platform like desktop web, and ignore the rest, but you do so at your peril because 60% of all web usage is now via cellphone.
Contact an owner of a web development company and trade services. Give him some of your services for free for tradeoff for him developing your app. Or a happy functional mixture therein.