I suppose, to raise an argument that hasn’t already been offered, would it be fair to say you are trading the concern of “my new forum will look new dead” with “my new forum will look abandoned” ? I can only assume you will eventually stop actively participating in the charade, regardless of whether you choose to be open about it later. Do you worry about the forum seeming to have a whole bunch of people who… appear to have completely lost interest in it and left? The way I see it, it will almost certainly seem very artificial (which will give off a creepy vibe) or else it will look like the majority of users don’t stick around. Neither seems to be a great result.
I used to be the sole Community Manager for a newly founded indie dev studio. I know what it’s like to feel like I’m talking to the wall; few to no responses, and analytics showing few passive readers. Long-term, I think the best thing is to focus on treating the problem rather than the symptoms.
Some ideas which may or may not be a good fit for you and your situation;
Mention it to one or two people you know offline, say you’d really appreciate it if they could drop by the odd time.
Focus on long-form posts that people have a chance of really getting interested in and responding to; sometimes quality is vastly better than quantity. For engagement, a single post the user is immersed in is worth hundreds of posts that just make up background noise.
Discreetly ask staff / moderators of tangentially related forums or subreddits if you could maybe post there about the new forum you’re starting. Be humble in posts that are permitted - don’t give people a false impression of what to expect.
Consider doing a couple of giveaways that encourage active participation. If you don’t have a budget, this could be for ~free things such as their own custom title / a unique avatar (if restricting most users to a pool of pre-selected images) / a shout-out on some page or another. It’ll incentivise people to get involved, and will ultimately become one of the first stories of your more community - years from now, new users will be asking about why User X got Reward Y and hear the tale of your community’s early days.
If it’s not rude of me to say, try to accept where you and your community are. There are people out there who will be more interested in joining your forum during its early days - people who like to feel like they’re helping to form a community, people who have opinions and feedback on various decisions (e.g. site settings or moderation policies), and others still who actively prefer smaller communities where it takes less time to catch up on recent discussions.
Every founder of an online space has been exactly where you are now. If so many others have succeeded, there is no doubt in my mind that you can, too. Try to be genuine, open, and welcoming. It will give off a much better vibe than a bunch of accounts which just seem to have too much in common (posting hours, style of writing, interests, registration date…) to seem natural.
The idea here isn’t exactly bad. It’s a technique known as “salting the jar”. The problem is that the suggested solution involves duping your audience – which might pay off in the short term, but at the cost of your credibility. This means you’ll also be a bit paranoid of people finding out(not fun), and should they find out, then they’ll feel like you and your platform can’t be trusted. Repairing that is a bigger job than preventing it.
Others have touched on a real solution here: Start with enthusiastic people first
This is my “Rule 1” of getting a group together, whether it’s friends or for a community. That means finding and recruiting the people who have already expressed some desire to have something like this. To begin with look for people who match at least two out of the following three criteria:
Note, “core topic” here denotes the main focus/theme of the platform.
Clear long term interest in the core topic
a. They have been involved in that kind of topic, or done that activity for a long time
b. They have heavily invested in that topic, such that they are likely to have an interest for the next few years
c. They have had long term interest in abstractions/parents of that topic, or similar topics(e.g. if football is the core topic, then “sport” would be an abstraction/parent of that topic)
Desire for a platform to discuss the core topic
a. Strong opinions about the core topic
b. Desire to teach about the core topic
c. Desire to market to people with that interest
d. Desire to learn about the core topic
Some form of investment/interest in you as a person
If you can find about 20 people who have two out of three of those traits then, so long as you listen to their feedback and adapt the platform accordingly, they’ll begin to bring others to the platform too.