I was a mod of a small niche reddit sub for about six years. When I started working on it, there were only about 200 subscribers and it was a pretty quiet place. Over the time I managed it, I had to work the group to get them interested. I'd regularly post, comment and like whatever was happening. But at the same time, I'd do searches throughout reddit to look for like minded people and just let them know my sub existed. No big marketing push but just a little reminder that my sub existed. I'd set out private messages to people and connect with them .. about half wouldn't respond .. a quarter would say they weren't interested but about a quarter would say thanks and that they weren't aware of the sub and would have a look.
After doing that for four or five years, I grew the sub from 200 members to 2,000.
I also learned that on any social media about 90 percent of users are just lurkers who like reading stuff, liking stuff and maybe once in a while commenting. It's only about ten percent of the group that are active, comment, post new content or even create new content. The larger your group, the larger that ten percent becomes and the more content your group generates and the more activity happens.
Keep working it ... it's all up to you in the early stages, you have to put in the work to contact people, encourage them to join and talk and chat with your base to keep them engaged. You create the content or highlight new stuff or keep posting content you find and share to your group .. all your users are there ... they are the 90 percent, you are the ten percent right now.
As your group grows, eventually there will be one or two people that will be enthusiastic and they will help with content ... then as the activity grows, there will be a few more active users who will post and comment regularly.
Your group will never suddenly one day jump to 10,000 users and your community becomes a hive of activity ... it grows organically like a plant in your garden. Right now it is small and fragile and anything can bring it down ... you not tending to it will mean it dies. But if you water it, tend to it, look after it eventually it will grow into something big and there will be many people that will come around to help you with this enormous garden or field of crops that have sprouted from your activity.