AFTER COMPLETING THE REVENUE PRODUCING PORTION OF THIS TRIP THE COMPANY PRESIDENT CALLED HIS COMPANY OPERATIONS AND TOLD HIS SECRETARY TO SEND EVERYONE HOME SINCE IT WAS A HOLIDAY. HE WAS GOING TO RETURN THE ACFT TO ITS HOME BASE HIMSELF. THE PLT DEPARTED VFR, AIR FILED AND FLEW AN IFR FLT PLAN TO THE FINAL APCH FIX TO THE CLOSEST ARPT WITH AN INSTRUMENT APCH, CANCELLED THE IFR FLT PLAN AND HEADED TOWARD THE HOME ARPT VFR. FOG AND LOW CEILINGS WERE IN THE AREA AT THE TIME. THE ARPT WAS EQUIPPED WITH RWY LIGHTS BUT DID NOT HAVE STROBES ON EITHER END, IT WAS LOCATED IN A VALLEY. AN ACFT WAS OBSERVED EAST OF THE APT LATER IN THE NIGHT. IT HAD ALREADY PASSED THE ARPT AND WAS IN A TURN WHEN LAST OBSERVED. AN ALNOT WAS ISSUED DURING THE NIGHT FOR THE MISSING ACFT. IT WAS DISCOVERED THE NEXT DAY ABOUT ONE-HALF MILE WEST AND NORTH OF THE ARPT, ON THE SOUTH-WEST SIDE OF A MOUNTAIN.