I have no experience with snowmobiles. i have always used skis or snowshoes, but why would 2 to 3 feet of snow "stop" a snowmoile? It must have been an extremely powdery snow?
Colorado is famous for temperature gradient snow where cold
temperature cause the
transformation of snow which produces powder-like snow. This "sugar snow" can set up conditions that cause avalanche and
also trap snow machines.
When searching for the lost in snow country, often it is important to use the same mode of transportation as the lost people. If you are looking for a snow mobile, use a snow mobile
for searching as it can travel far and will access the
same terrain. Ski searchers can get into places the snow machine
can't get to as a lost person on skis or snowshoes might very well travel following the path of least resistance (steep and deep, river bottoms) that would trap a machine.
When looking for a lost skier, being towed on skis by a snowmachine to the point last seen is a useful combination of the two methods.