Who are you looking to have join? What would they be interested in?

Since it seems that many users came here in the wake of their past communities being closed, destroyed, banned, ruined etc, maybe it would make sense to keep an eye open for endangered leftist spaces and give them an invite. These are moments when people are actively searching for new spaces and have space to fill in their lives.

Here is a general purpose list of websites that may soon close: https://wiki.archiveteam.org/index.php/Deathwatch

But leftists are always getting kicked out of wherever they are at.

One element of hexbear that the existing users really enjoy and value is the cliquishness. Its a lot of in jokes and references. Constant callbacks to specific threads that happened years ago and either aren't online or aren't findable. Having been here for a year and a half I can mostly follow the main themes but lots of it wooshes past me. People like to pull rank and show how long they've been here. Once you are in a group like this it is extremely comfortable and nice and you feel connected to other people.

I am not saying this as any sort of criticism. It is what it is and overall I like it. but it is inherently difficult to recruit people into such a scene. New users are at a disadvantage. Plus there is the dynamic state of behavioral expectations and current meta discourse.

If the site wanted to make an effort to grow, it would need an idea about how facilitate integration of new users.

I can't imagine a successful recruitment campaign not leading to hella drama. It would inherently change the character of the site.