They are interested in them it is in searching for them they find the undercurrents - however they don't have to find out for the mystery to be concluded. The closure can come either in the form of they are dead, they are alive or they never find out. Only one of the people actually needs to be found for the story.
Hehehe! I think you should consider writing a murder mystery with a comic approach at least at some point, Are they all connected to each other, like a group of people from example a train or bus journey or people staying in a hotel or are they all separate cases? I sort of like the idea that they don't know each other but are somehow connected to each other against their will.
I'm not sure your story is a "murder mystery" or a "detective mystery" at all, since the mystery of the missing/dead persons isn't at the centre of the plot. It sounds more like an adventure story. The only way I can think of this going wrong, is if the reader expects the story to be about the murders/disappearances and gets disappointed when they're not resolved in a clever way.
Definitely look at what the reader will get out of the story. You don't want them throwing down the book in the disgust when Nancy comes back in the last chapter and everyone says "whew, I thought you had been horribly murdered but here you are safe and sound. Please phone in next time, your mother and I were worried sick." Reminds me of Twin Peaks. Originally it's about "who killed Laura Palmer?" but after a while people just got into the story and the wild ride (and probably the self-medication while watching each episode). I think it could definitely work as long as the journey is so good that people don't mind the destination.
They are all connected to the death/disappearance when my lead detective was ten. The maid works at the hall and has a connection to the wife of one of the missing detectives. I was just going to query it as crime/detective fiction anyway. The undercurrent is a crime.
