There is probably no other way than to seed it. You can do this with outright bots or contractors from fiverr, but people who grew up with the internet are very good at spotting inorganic growth.

I'd start with a slow rollout to friends, family, colleagues and even LinkedIn acquittances. You'd be surprised how many people are super eager to be the first to test your apps, even with a generic cold message like "hey, remember me? I built this cool app, wanna try it out if you have a minutes? I'll send you money to cover the fees."