I am planning to run a game of Nobilis on roll20 but I am having trouble finding people for it. Is there some sort of advertisement technique I can use in order to recruit players for my game?
It might be helpful to create a game ad at a gaming site. Myth-weavers.com and giantitp.com are good examples of gaming forum sites where gamers regularly go to find games. They are mainly dedicated to play-by-post, but myth-weavers allows advertisements for any games that use the myth-weavers site or discord server in some way. If you choose to use the myth-weavers site, I would recommend creating a game forum for character creation, ooc discussion and meeting/game coordination.