Cats are very clever about hiding, especially if they're not feeling well
or simply don't want to be found. You can try scent trails/beacons -- such
as unwashed clothing placed at various intervals out from your house, and
walking barefoot out from the house in a spoke pattern. Whether or not
this is practical depends on your current climatic conditions. (Barefoot
with snow on the ground isn't terribly comfortable.)

When my boy got away several years ago, these techniques may have been
what finally got him back after nearly a week (which lots of searching and
calling over those days); hard to know for sure. But it was a day after
attaching socks to the backyard fence and walking 1/4-1/2 mile spokes
barefoot from the house that got him to reappear. (And yes, that walking
was rather painful.)

Good luck,
Frank