ASK HN: Startup the chicken and the egg problem

We are implementing an idea that the users are the content providers, for this reason the more the active users the better the quality and the value of the product hence better chance for more users to use the product hence the better quality and the loop!

It is always easier to get funding with a prototype ready with active number of users than selling the concept/idea to the investor with nothing to back it up that it would work but with the above chicken and egg problem described what approaches would you take to deal with it?