This is an interesting discussion. In early 2000's i grew a forum to 25,000 threads and 6,000 members with little effort. I agree, usage of forums has changed. I think there are two succesfull forum models...
1) You have a product or technology and the forum acts as a support portal and portal for collaborative development
2) You have a community where active recruitment is a part of the community model, and special rewards for recruitment (such as gaming clan etc)
Of course, I'm biased because Im relaunching a gaming community.
These days, it seems the hobby forums, e.g. "come talk casually about horses" are dying because social media is filling this void. For almost any subject I can just go find a facebook group, where thousands of people are talking about a certain subject every day because they already use fb.
But say I have an app for horse owners. Those users will use a forum because they want the app to develop positively.
Just my 2 cents
After being "away" (e.g., taking a break from engaging in most activity regarding forums - mine included) I decided to go back over my "watched threads" list here at Woltlab Forums; and that was a good thing because it has given me an opportunity to look at past topics and discussions (and my responses) in a new and refreshed "light".
Ellionator - I like what you had to say in #'s 1 and 2. I think you have correctly identified the "king pin" to a establishing a successful forum.
I would add here that I personally believe there can be at least one addition made to those two points you made - I will elaborate further on herewith. But first I would also make some observations regarding the area of "competition" - that being Social Media. Actually, it is in the truest since not a competition but rather a distraction!
Unless Facebook and Twitter implode sometime in the future, those of us who like forums (and also do not believe 'forums are dead' - as a few persons have stated) will just have to accept the fact social media is a "force" that must be recognized, but also understood as to why it attracts many people.
1) Social Media - like Facebook for a prime example - attracts most people because they don't really have to think for themselves - especially when it comes to forming new ideas and making independent, unique decisions entirely on their own. Instead, there is this built-in ready-made social response "formula" that enables their participation without having to make any extensive and well thought out contributions.
[One person here on Woltlab Forum said it quite well I think: Most Facebook users are mindless robots trolling along like sheep; or, sheep being herded over the cliffs - and gladly to so.
2) And Twitter ... well here we have a bunch of people who engage in quick spurts of "tweets" without any thought as to what the consequences of
their tweets may lead to. Most couldn't care less - even those in "high places"! And as for actually engaging in any unique, thought-provoking one-on-one discussions of a complex or comprehensive subject with someone else ........... well, that not only didn't cross their consciousness, many also wouldn't know where to begin in taking part in subjects and discussions which require not only concentration of serous thought beyond a few seconds, but which also requires thoughtful, purposeful direction of the thought processes.
Now for that "one addition" I mentioned I would include here:
From my experience with interaction on Forums - and I have been a member of various types/formats of forums - from highly technical to the "adult" sites - there is one element that many (but NOT all) Forum Administrators who actually under-cut their own success regarding making their forum attractive to a wide audience. And when I say this, I am fairly sure I am going to ruffle a few "feathers" here, but I am going to say it anyway:
1) For some illogical reason, many (but NOT all) forum administrators have an unbending, unreasonable opinion (and with it the implementation thereof) that allowing a Forum Member to refer to, AND / OR include a LINK to, a blog, forum, or a website they are also an administrator of.
Why alienate, restrict, and suppress a Member's activity simply because that person offers something that someone else (another forum member) may be interested in? What is the Administrator afraid of? Such a narrow minded approach is foolish at best, but worse, it is also self-defeating.