I’m not sure – mine didn’t fail!
The two things that DID work which were vital (so if you didn’t have or do them you’d fail) were a proven concept, and a lot of manual, granular hard work.
A year before launching the forum, we started a blog to build an audience. We started a (passive) social media following as well, but it was of little relevance. I started connecting with people that gravitated to the blog and researching the feasibility of a dedicated community. This had the added benefit of the vital relationship building required to form a founding group.
It became clear that the content that resonated best with this early group of followers was anything to do with transitioning into a UX career from another discipline (UX was very new at the time – still is as a recognised career, really) so we honed in on that for the community concept. Since then, as the audience has grown up with us, the concept has diversified slightly to include intermediate to advanced content as well.
Once I had a core group of people that regularly commented on the blog and responded via social media or emails, I started lots of personal communication. I also contacted influencers in the wider niche and got buy in from them, which has paid off in spades now because I have a pool of big names that I can use for Q&A sessions etc.
When I launched the forum (on vB cloud), I sent out an email to the 5k people that had subscribed to the blog. A couple of hundred of them signed up and I had 20 ‘Gold Members’ (the strong relationships I had built) who were armed with questions to seed. For every question, I personally reached out to someone else that I’d met and asked them to answer.
It was probably about 4 months before I stopped having to answer (or personally find someone else to answer) every question.