Not sure if this is a saying or just a statement, but one thing I find difficult is when you are sincerely inquiring about someone and the give you the " I'm fine" when you know they are falling apart or disturbed about something....gets me every time!

Sally we definitely use it here in Canada. Usually we say it when we know we had something, let's say our keys, in a certain place, say the dish by the front door, and now they're not there. We say they've gone missing. It's saying, ok what have you people here done with my stuff? accusing you're family, or friends, of moving your stuff, and telling them you better bring in to me right now. If no one lives with you, it means your putting yourself down for mislaying them somewhere, unless they grew legs and walked off themselves.