I Know Where The Lingerie You Lost Is
I'm an expert at losing lingerie, therefore I know where the lingerie you lost is. I'm like a psychic, except instead of being psychic I'm going to use rationality and experience to help you and it won't cost you $5.99 a minute. Ha! Take that psychics!
Behind The Washing Machine / Dryer
If it's been more than five minutes since you looked behind the washing machine or dryer, there's a decent chance that your lingerie is behind one or both of these appliances. There's definitely a sock there.
In The Stuff You Still Haven't Unpacked Since You Last Moved
If you've ever moved in your life, you have stuff you never bothered to unpack since you last moved. You clearly don't really need this stuff, or want it enough to actually unpack it, yet you refuse to just bite the bullet and get rid of it. Odds are 50% of the things you vaguely remember once having are there. The other 50% are still in the bottom of the closet at the last place.
Under The Couch / Under The Bed
You didn't put it there, but if you have a pet cat or dog. I'd stake my money that they're lingerie hoarders just like the rest of the animal kingdom. If your dog is Labrador sized, your may also have to consider the possibility that your lingerie may very well have been eaten. Hanky Panky lingerie in particular seems to attract the palate of un-discerning large canines.
Your Roommate Has It
Whether your roommate is male or female, if your lingerie is there one moment, gone the next and you've checked under everything you own, and some things you don't, like the house, then there's a decent chance that your roommate has it. Do you want it back at this point? Probably not, unless you're a Forensics Major looking for an excuse to use a black light.
Your lingerie didn't go on holiday by itself, but it decided to stay on in the Airport in Frankfurt, Germany, where you were inexplicably forced to take a connecting flight. Unlike you, your lingerie will never need a VISA and its prettiness is all the auslander ausweis it needs.
At The Gym
You bought a membership, a padlock, a water bottle and a sweat towel. You used the gym once, found it to be an incredibly horrific experience and left your lingerie accidentally locked in a locker. By now your locker has been cut open by a snooty chap or chapette with less than 15% body fat and is being snickered at even though it looks perfectly fine. Jerks.