Assuming you can find one ski, use it to search for the other. I use the tail of the ski, cut back and forth across the fall line, as deep as you can.
In my experience, the ski often goes WAY farther down the hill than you think it would have - if the ski released in a fall, IE, it did not just STOP, it'll often be pretty far down the hill from where you wound up - and the snow won't always have a depression to indicate that the ski tunneled under.
For deciding where to start looking, think about when it came off - if you were tumbling, it could be anywhere. If you bottomed out in the snow (into a stump, for example, as I did last weekend
, it is probably above you. If it was a backwards-twisting fall, it is below you.
Skis get lost sometimes. Not forever, naturally, but until spring. If you have friends, and it is not turning up quickly, and it is reasonable to ask, tell them to make another lap & help you find it by traversing back and forth where the ski might be - crude, but effective.
Powder cords/straps can work, but PLEASE tuck them in
. I tried them once in 86 or so, found them to be more of a hassle than they're worth, especially if you're riding a tram/gondola/hiking/need to take your skis off frequently.
Binding screws are very, very effective, but too much of a good thing is a bad thing
. Approach with caution.
I've never lost a ski (and I've had lots of powder days - more than most, I'd wager). I have spent up to about 10 minutes looking.
The biggest thing I've learned is to look farther downhill than you think - I found a guy's ski at Snowbird that was probably
100' below him (not vertical feet), he'd been there for two trams, figured I'd stop and help him out, started where he fell and traversed back and forth, about 20' each direction,
going slightly downhill, until I found it - it was WAY below him. There was a fair bit of dry, light (even by Utah standards) snow on a fairly firm surface - the ski just dove and kept on going.
If it is not "right there" figure out which way the ski was likely to go, and start going down. It HAS to be there