Yes, anyone could 加入 your club, if 由 that 你 mean becoming a 粉丝 of it. It's not possible to restrict any 潮流粉丝俱乐部 user from becoming a 粉丝 of any club on Fanpop. Of course, 俱乐部 aren't owned 由 any particular user, even if that user created the club, so it's not really "your" club any 更多 than the 潮流粉丝俱乐部 Users club is "my" club.