As far as I know, there's no tool that can automate the whole process for you in terms of republishing posts. If you want to republish your post somewhere, you'll have to do it manually. I'd say that being an engaged user within the specific community will definitely help. E.g. If you post a link on Reddit, and there are some comments about the project, I'd make sure to respond to them. Also, reacting to other people's projects and leaving your comments helps build credibility and karma.

In terms of sharing things on social media, there are specific tools, but they are mostly paid. E.g. Buffer.

Thanks!