in my experience after decades of building online communities, i find what works best is finding people who have a good personality fit to the community then pitching them a feature that might interest them.
wetfish is a little different because its essentially misfits. so the handful of people i've invited who stuck around, are very much "misunderstood by the world" but good hearted and kind.
i don't think any of them use the forums or mumble or anime night or any of the advanced offerings that are unique to wetfish.
anyway i shit post a lot. less than i used to. for a while wetfish had a discord server and i tried to recruit ppl to it. then i gave up on it bc it wasn't active.
i don't know why people stick around. i just want a place to shitpost :-)
question for you, OP: why do you want to attract new wetfish?