It really depends on what you're building here. If you can do any part of your product manually, I would suggest doing that in the first version.

The absolute fastest way is to hire a contractor to get it done, but that can be expensive. If your first prototype can't be built with a prototyping tool (even a Keynote presentation) and it's too expensive or difficult to build on your own, you have to convince other people that you are solving an important problem, that your solution solves that problem, and that you have the right team to do it. VCs in a seed round will care more about the team than the idea, but crowdfunders will care about both. And obviously getting designers or developers to join your team for equity will require convincing them of all 3.

Happy to give more specific advice based on your app thrugh a Clarity call!