So to make things more clear, I will summarize:
I have everything (including a business plan, development plan, technologies know-how and general business and specifically experience in creating video games, as part of my several decades of professional experience working in the IT industry and my education) that is required to start with turning this idea for a MMORPG into a commercial (and according to the figures commercially successful) product, minus the funds, some things to take care of on the business side and the required "talent" / HR.
I am looking for information (tips, ideas, ...) on how to address the HR issue, specifically where to post on the Internet to advertise the opportunity to an as large as possible (yet suitable) audience, preferably free of charge. To add that "talent" to the project is important so that a prototype can be produced to attract funding.
Advertise as large as possible is incongruent with free of charge.
I've worked on games that have a DAU of around 150,000 players. We invested tens of millions in the game every year. We have server farms in three continents. But even that isn't really enough players to be considered "MMO" status. MMO has a meaning, and it involves lots of money.
That first "M" has a very important meaning that many people forget. That first "M" can really only be achieved by a global presence that in practice is quite expensive, approaching a 9-digit figure in money. Perhaps you simply meant a more general online world?
If you honestly meant MMO, then I will assume your business plan details things like how you intend to develop your server farm, how you intend to provide global 24/7 support, global billing, global taxes, global translations, global privacy laws, global security regulations, global game ratings, and many things beyond simple game design documents. Simply creating a game (production) is relatively easy. Post-production costs and lifetime product support generally dwarf development costs.
I'm really not sure how in your business plan you intended to get your tithe-of-a-billion dollars in funding. That's the thing most people in the discussion are confused about.
So if you mean a real MMO, assuming you have already used your networking skills and talked with all your professional contacts you have developed, you will need to spend money. Lots of money. Around fifty million dollars worth of money (at least) over the first three years.
You have "several decades of professional experience". This means you should have a network of personal contacts that extends to several hundred people. Recruit your first round of leaders from people you know can do the job and are willing to take the risk. If none of your friends and acquaintances are willing to take the risk, think about why.
You incorporate your business (costing money) and start paying people (costing lots of money) as a startup.
After you and your contact network has been questioned, you need to hire one more person: An HR specialist (costing money).
You and your friends (the contacts willing to join you) will form the core team. Any skills you don't have among you get listed and given to the HR specialist. They will scour the internet (costing money) and use their network of headhunters (also costing money) to hire people with the needed skills (which costs lots of money).
If you have to ask, you probably aren't ready for it. If you don't have the experience or business acumen to hire the first core group of people, you are absolutely out of your league for a real MMO. It is a very ambitious project usually approaching a hundred million dollars. First get your feet wet with a few million-dollar projects.
So, did you mean a real MMO, or did you mean a more simple online game?
If you read the Networking Forum FAQ, there is a link to how to develop a basic online world server in under a day, and develop a simple isometric online multiplayer world in less than a week. The server in the FAQ can probably support around 500 concurrent users.
If you don't think "MMO" you really only need one or two programmers, a modeler, and animator, and some audio. You will fill the role of designer and producer. A simple, professional looking non-MMO online world can be put together by a small team in just a few months. It has been done many, many times. Again you can likely get that from your network of co-workers you developed over decades of professional experience. Building it is the easy part, selling it and supporting it is much harder.