I think game jams are a pretty solid idea, and youtube videos going over weekly dev-logs / updates, as well as introductions to how Steem / Steemit works and how Utopian-io & Open Arcade work will probably attract some people.

Maybe even try to partner with game developers and have them post generalized game-dev tips & tricks onto your youtube channel [ so, not necessarily game-engine specific, but things like "how to do pixel art for games", "how to master game-feel", "how to market games" ]. That way, when people search for these topics, they may come across your channel, and if they visit it looking for more content, they'll discover Open Arcade.