Pay them (https://news.ycombinator.com/item?id=19630181).

Other reasonable suggestions include: - Post on producthunt - Post on reddit - Google Ads - Facebook page - Cold-emails - Word of mouth - Business cards - Scour the internet for forums related to your web apps

The best success I've had has come from winning the HN lottery, I got on the front page. Otherwise paying people was 2nd. I don't have a 3rd option that has worked well enough yet.