I started with writing open source Ruby gem https://github.com/ArturT/knapsack for running tests in parallel on CI and later I gave a talk on local meetup event for Ruby developers.

With time I wrote more blog posts https://docs.knapsackpro.com and shared on Reddit, Twitter, LinkedIn profile or Ruby groups. From time to time posts landed in RubyWeekly newsletter.

Also asking users for recommendation might help.

I connected with each person on LinkedIn I talked to or who signed up and I followed them on Twitter. People who like your product can easily see you publish new content and can like or share it.