I agree traditional business plans aren't necessarily required but if there is no monetization model then I can only assume that you are trying to make a massive audience play. (Think "Instagram" and to a degree "what's app") At the very least I would put together a lean canvas which will give your potential investor the confidence that you understand your business, your app, your market place and your customer and how you are going to leverage that knowledge.

Check out http://businessmodelgeneration.com/canvas and https://leanstack.com/

Happy to talk to you in a call if you need more detailed advice