I assume that you have retraced your steps like where you were when you saw it last? You checked under the bed ... under all couch and chair cushions ... under all couches and chairs ... under the dirty clothes on your bedroom floor .... under all the loose papers on your desk/dining room table/kitchen table or any other flat surface where papers/junk accumulates? How about all blankets & linens on or off your bed? Did you check your car? Don't forget the back seat, under the seats and in the trunk.
I came back from a bike ride a year or so ago and quickly put my bbphone down in that dark basement. I could not find it. And while I could call it, it would go to voice mail before I could track its location. Now I have "find my phone" and it makes a disturbing racket if I misplace it.
Maybe we all should set an alarm on the pb for a particular time of the day. At least during that window (set time) you might be able to find it. Hmmm, 3AM, not much competing to make noise at that time of day!
Back to Cokiak's resolution - don't you hate it when someone else "cleans up!"