It helps to start blogging about things that are related to your product or interesting to your target audience. I got the first users by writing about text-processing tasks that you can do with regular expressions: https://www.abareplace.com/blog/
What we are currently doing: 1) Cold outreach to power users - to convert them into affiliates. 2) Cold outreach to individuals who have target ICP communities. 3) SEO for more long term (not for the first 500)