I first learnt about Touhou watching
this LPer sometime in 2009 or 2010, but it didn't interest me at all back then and the fact that several of the games he played were littered with references annoyed me more than anything. The only characters I picked up were the EoSD crew and Reimu/Marisa, though.
Then late 2011, I met a moderator on the Pokemon Online server I frequented (and later got promoted on as well) who used a lot of Japanese names as his alts, which later turned out to be names of Touhou characters (mostly PCB and IN, but Eiki and Byakuren and I
think Parsee were also among them), but I didn't care yet, either, even though we were friends on the server. He did convert another guy to Touhouism, though, and this guy later convinced me to try out Touhou in summer 2012. The reason why I gave in was that I had listened to UN Owen and Necrofantasia Synthesia remixes a bit before that.
I started with PCB, later IN, and it was really cool to see all those familiar names in-game. In hindsight, it was kinda funny how I could easily remember names like Keine Kamishirasawa and Shikieiki Yamaxanadu, but had trouble with Kanako Yasaka, all because the latter wasn't a name this guy used.