Ask HN: How do you get beta users?

You're solving a problem for people so start by thinking about what kind of person has this problem - are they in a specific job or industry, are there subreddits that overlap those people, maybe you can use facebook and google ads to hook them, or twitter to reach them directly. Maybe you know some of them personally. A small number of your ideal users can make great beta testers and then customers.

Agressive acquisition. I remember that Reddit had 0 users for a very long time and the owners were just creating fake accounts making fake posts and acting like it was populated... then suddenly people thought hey this is cool and started joining in. Then they hit critical mass.

So, aggressive acquisition.

Ask friends or existing customers.

Failing that, I create a marketing page with screenshots, explanation of why it's cool, and a "register your interest for early access" form.

Then try and do some SEO so it appears in searches (Google Webmaster Tools help me see if that's working).