My cat went mising a week ago, and now my mom's went missing a couple days ago. What's going on?

I have put out fliers and contacted our local vets. I have also registered at missing pet sites. Both of them are spayed and it is out of character for either of them to wander too far from the house. My cat has been stolen once before but in a different city. We haven't heard any coyotes or mountain lions recently, so i dont think they were eaten, and we haven't found any cats by the road. It's a bit too much of a coincidence that both of them went missing in the same week. They are indoor-outdoor cats and we are all upset. I don't know what else to do to get them back...please help if you have suggestions or maybe some answers as to why they are missing.