I just discovered this platform for finding collaborators for projects on HN this morning, funnily enough: https://www.codekhub.it/

It seems very small at the moment, and very focused on developers, but it's an interesting premise. I'm a blogger, not a developer, so I don't think I'm quite the target audience.

I find discord is very helpful for this.

Find servers that are used by people in your desired audience and there is usually an appropriate channel to post in.

Let people know what you are doing and what you are looking for and interested parties will message you.