Here are some ideas...
1) I always am looking and panicking over whatever it is that I have mis-placed. I am not Catholic, but a Catholic friend told me that St. Anthony is the Patron Saint of the lost (or lost things?). Say "Tony, Tony look around what was lost, must be found." And then STOP looking. The lost item usually turns up shortly...when I am not so frantic.
2) Go out to your car, walk from the car to the house. Walk in the front door. Look around (and this is very important) on all surfaces AT EYE/HAND LEVEL. That might sound obvious, but I can't tell you how many times I have misplaced a cap, looked for it where it is supposed to be?...and then found it on a corner counter/shelf in the kitchen. So, walk from the door to wherever you normally go when you enter the house, kitchen, coat closet, bathroom, laundry room... Walk slowly around the house and do a circuit...look on kitchen counters, bathroom shelves, bookshelves, computer desks, at eye/hand level.
3) Did you have any groceries with you or presents when you last entered your house with keys in hand? Check wherever your gift stash is, or wherever the wrapping paper is kept. This next might sound funny, but check your freezer and refrigerator and cupboard/pantry. You might have put the keys away with your groceries.
4) Offer a cash reward to anyone in the house who finds it.
5) Check whatever coats/outer gear you were wearing when the keys disappeared. Check the LINING of the coat, maybe the keys fell through the pocket into the lining. If wearing boots, check them. Maybe the keys fell down inside the boot or whatever shoes you kicked off at the end of the day.
Good luck, when you find them let us know all about it.
agnes!