Ask HN: Where to find agencies/startups who could be my first few users?

I'm a developer as well and for me I'd say the most effective way to reach your audience is to cold mail them about your product and services. Cold mailing them in a way that's not spammy and instead makes them what to know more and reach back out to you. And don't just limit yourself to cold mailing, if you don't know someone's email, you can hit them up on insta or twitter for cold DM's, but again you need to be careful of what you say and how long your messages. Chances are they get a lot of similar messages, so you need to act quick in a short message while still attracting them to your concept