If it's a canon that I know friends are also into, I ask them if they're interested in playing any characters from it, or tag them if they already are playing from the canon.
If it's a "fad" canon that has a bandwagon attached (an ongoing show, something which just finished a run, etc) I look for characters from it I am interested to tag on BS. Eventually some do stick around, and I've met a few friends this way.
If the canon is new only to you and/or has no bandwagon, then you can either (1) try to get friends interested in the canon so they will play castmates or (2) tag out crosscanon and hope you are engaging enough to have the players you tag look into the canon, thereby leading to (1).
Re: HOW DO YOU FIND NEW CASTMATES?
If it's a "fad" canon that has a bandwagon attached (an ongoing show, something which just finished a run, etc) I look for characters from it I am interested to tag on BS. Eventually some do stick around, and I've met a few friends this way.
If the canon is new only to you and/or has no bandwagon, then you can either (1) try to get friends interested in the canon so they will play castmates or (2) tag out crosscanon and hope you are engaging enough to have the players you tag look into the canon, thereby leading to (1).