Picking an existent audience

Starts are always hard. But you can get traction faster than you think.
You have a project, and you want to reach as many users as possible. Therefore, you have two choices. You can -one- define your target and reach them through several platforms, or -two- reach an existent audience and boost your growth.
Picking an existent audience allows you to save time and boost your growth.
Paypal did this with eBay. Airbnb did this with Craigslist. And so many others found growth in existent platforms.
Is there any place where you can find an existent audience that fits your target requirements? If not, take a second look and find ways to reach’em.
If you can find an existent audience, it will boost your growth.