If you're looking to launch a project one of the best things you can do is try to get feedback early on. This can only happen if you understand what you're trying to build and who your target audience is. How do you find all that out?
You aren't going to be able to post an instant success on HackerNews or ProductHunt. It does happen sometimes, but very rarely and only if you already know what you're doing. For the rest of us, it's important to prepare by testing ideas with smaller communities. Many of these larger projects that end up successful on the more popular sites do so by taking advantage of network effects. That is to say, the people developing them already have a reputation they are building on in their own social networks. Once they actually go to launch a project, the following they already have helps amplify the product through network effects.
You can find smaller communities such as https://www.indiehackers.com/ or https://betalist.com/ to post your product journey. Even here on https://dev.to/ is a great place to test things out! Otherwise, if you have an existing social network following, that's a great place to start too!
In the beginning of your product lifecycle, you aren't likely to find anyone running to sign up for an incomplete idea. You also don't want to wait until you launch completely for people to sign up then either. The old saying "if you build it they will come" doesn't work like some fairy tale it's made out to be. You will need to network, and gather feedback.
Gathering feedback and sending out e-mails/invites/direct messages isn't so bad though! This means you can scale at a slower pace than your system is likely to handle in the beginning. By slowly seeding out invitations and gathering beta users, you build a window of time to ramp up development. This buys you time and actual active users. Of course this also has some tradeoff concerns with potential competitors wanting to figure out what you're doing. You'll know what that looks like in terms of the type of feedback you're getting. Just be aware of this.
Keep your community in the loop. There are ways to go about this that don't involve spamming everyone. You can, for instance, start a newsletter. I've seen dozens of small startups in Indie Hackers use this approach for even the smallest of ideas. You would be absolutely surprised how far these type of product journeys go, even to MRR territory. Aside from that, another method is to engage with the community itself. Find out what sort of niche you are looking to capture and perhaps talk to those people. I've used apps like https://headwayapp.co/ to keep users in the loop before for example.
Many of us have used https://www.atlassian.com/software/jira, or https://www.uservoice.com/ to gather support into your application. There are dozens of services out there to help; you could even add a https://slack.com/ button to your website so anyone can join the community to support it.
Don't be afraid to get yourself out there (metaphorically speaking please). You may be surprised that there are plenty of niche communities with small user bases who are willing to try out what you have to offer or even just to follow you on your journey. Much luck!