The pilot had filed an IFR clearance. While taxiing to takeoff, he requested and received a clearance to climb VFR on course, via Victor Airway 2, with instructions to report when reaching 10,000' MSL. This was the last communication received from the pilot. When the aircraft did not arrive at its destination, a search was initiated; however, the aircraft was not found until 11/28/87, when it was discovered by a hunter. An investigation revealed the aircraft had crashed in mountainous terrain about 14 miles west of Missoula, MT and 8 miles south of the airway, while in a steep descent. Impact occurred at an elevation of about 6400'. No preimpact mechanical failure was found. The 1352 MST weather at Missoula was in part: 3000' scattered, 4500' broken, with mountains partially obscured in clouds and isolated snow showers. An AIRMET warned of occasional moderate rime ice in clouds and precipitation above the freezing level to 15,000' and occasional moderate turbulence below 16,000'.