I've been a part of the board of TEJO during the last year, the umbrella organization that connects the worldwide Esperanto youth movement. That doesn't mean that is the only organization active in Esperanto, and each national organization has their own organizational structure.
Even though I've been in Esperantujo for a while, I still come across organizations and activists that I didn't know about before, like SAT. Even though I know about the biggest youth organization, maybe there are others that I have missed.