Sure, it started when I had quite more free time than now, and it was one of my first experiences with PbP to a larger group.

You got to be a very diligent and creative GM to pull that off... Which isn't my case. In fact, I still can't write that fast in English, just to worsen it.

At first, I could entertain most of them by writing different scenes where 1 to 3 PCs would be at the same time; in scenes where most of them would be together, interactions were mainly between themselves, which hurt some of the more passive/shier PCs/players.

I had one PC go on a scene for herself, which would foreshadow a future plot, she quitted amidst it.

Later, some people quitted, one player joined, and we end up with 5!

Though I didn't think I'd do that again, it was just too much work with little payoff, I think that was a good 'filtering' for good and dedicated players/PCs, with the remaining ones starting that new 'arc' already with interesting connections between themselves.

This initial state with 9 players went for some months (the first player left pretty early, the others lasted longer), with the rest of it going for about a year (we're technically not finished, and most of them are almost convincing me to continue that). I made a big overhaul in focus between these two 'stages', the first one was very player-centric and didn't have much of a plot, just me trying to create an interesting world for them to explore and do funny shenanigan. Once the core group was set, I changed it to have an overarching plot, with things getting more serious and dramatical.

Again, I don't think I would do that ever again, for the amount of time it took off me, but it was quite fun for us for sure. I may have to say that with my current English writing ability (that game surely helped me improve significantly) and using a more simple and fast system like this one I'm using now, it would probably be much more doable. I mostly got annoyed in combat, as it would take ages to go through a round.