"Somebody else mentioned this wasn't his first time..." Connor looks around, but he can't see the man in question from where he's sitting. "Nida, his name was. You know him?"

Maybe once you've been kidnapped from a world once, you're easier to kidnap again? Or maybe this is far more common than he could have expected, but everybody who vanishes is just a missing person, languishing in cold case files the world - or many worlds - over.