A couple of other suggestions.
Once you come to a stop and realize that at least one of your skis is missing, just collect your thoughts for a moment. Visualize your fall and try to remember if the ski came off early or late in the fall. Any clues you can come up with *before* you start searching might lead you to the ski more quickly.
Before you start your search, take one pole and mark the place you came to a rest. You'd be surprised how many people start zigzagging back and forth and up and down and end up searching too far away from the original fall. If you've marked your landing spot, you'll always be able to go back to step one.
My own experience is that if the snow is fairly deep, the ski is nearly always higher up the hill than where the skier comes to rest. Look above you and try to retrace where your line was, where the fall occurred, and where you've ended up. Usually, that will help you be as efficient as possible when you start your search. If it's untracked snow other than your line, your tracks leading into the fall can be a huge indicator on where to look.
One caveat on that: if you've got 10" of fluff on top of a very hard base, a ski can slide a long ways underneath the new snow surface.
If you're alone, search the most likely-looking areas based on your observations first. If the snow is deep and the slope is steep (what we all want, right?
), it'll be difficult to move uphill, but that's usually where you need to go. Use the "sweep" method with a pole or ski tail. The ski tail used to be better when we all used long skis, but a lot of the skis people are on these days don't have much tail behind the bindings. If your "obvious" search doesn't uncover the ski, go back to your mark and start a very methodical grid search (pain in the *$$).
If you have one or more helpers, do the grid search first but really concentrate on the area that your observations tell you are the most likely.
If the snow is deep and you don't find the ski right away, the area you're searching will get all packed down along with the ski underneath. Then, it's harder to sweep and it's harder to detect the ski and it just gets worse and worse.
What you do right at the beginning often gives you the best chance of finding the ski easily.