Interaction is definitely why I'm in fandom as well, and it can be hard to get much of that if you write in smaller fandoms, or for closed canons. I try to be the kind of presence in fandom that I would want other fans to be in relation to me: someone who interacts enthusiastically with others, who leaves comments on fanworks, and who participates in exchanges, challenges, fests and so on beyond the bare minimum requirements of the event.