This is a scary and sad story. I don't know what I would do. Maybe the people know, but maybe they really did find the puppy and had no way to find you, the owner
But also, I'm not exactly sure what the laws are on "unclaimed property", if she had ended up in a shelter they would have adopted her out to a family and I don't think you would have any claim to her.
Sorry for this difficult situation and good luck.