A different option might be to start with a base HTML template from ThemeForest (they have amazing designs) and then hire a dev to tweak it. Those templates are < $20 for a robust UI/html kit:…

Are you willing to spend money? You can incentivize users with contests/giveaways that are promoted via paid ads. You can also try to ask your own network (friends/family/LinkedIn, etc) and their networks for feedback.