1. Start by defining an Ideal Customer Profile and be very specific (for examples, Facebook started with Harvard students in certain social circle). A good way to know how to be specific is by using a framework to define your ICP, like this you know if you are collecting the right information or not
2. Once you define your ICP, depending on the framework you are using will have mapped where they usually "hang out" online and offline -> At the beginning prioritse offline more than online. You are doing things that don't scale.
3. Having that information, you then design a way to get in front of them. If you are going the "online" route, then it can be Paid Ads, it can be social media DMs, etc... I only recommend the only route once you know you have the right messaging tested by talking with users that became paying customers.
As a final note: try to get as many users that fit the same ICP as possible at the beginning, you'll want to seem a big fish in a small pond.