THE INSTRUMENT RATED PVT PLT FILED AN IFR FLT PLAN FOR A FLT FROM AN UNCONTROLLED ARPT AT NIGHT. THE ARPT MANAGER WAS AWAKENED BY THE SOUND OF THE ACFT STARTING & TAXIING. HE NOTED THAT THE RWY LIGHTS WERE ON, BUT WERE OBSCURED BY DENSE FOG. HIS HOUSE WAS APRX 150 FT FROM THE RWY. AT 0445 EST, THE PLT OBTAINED A CLNC TO TAKEOFF WITH A VOID TIME OF 0500 EST. WHEN THE VOID TIME HAD PASSED & THE PLT HAD NOT CONTACTED ATC, ATC PSNL CONTACTED THE ARPT MANAGER. THE ARPT MANAGER CHECKED THE HANGAR AREA & FOUND THE ACFT HAD DEPARTED. A SEARCH WAS INITIATED, BUT IT WAS HAMPERED BY DENSE FOG. SUBSEQUENTLY, THE ACFT WAS FOUND WHERE IT HAD CRASHED ABOUT 700 FT SOUTHWEST FROM THE DEP END OF RWY 27. INITIAL IMPACT OCCURRED WITH A 40 FT TREE WHILE THE ACFT WAS ON A HEADING OF 258 DEG. AFTER TRAVELING ABOUT 200 FT, IT HIT ANOTHER TREE ABOUT 26 FT ABOVE THE GROUND, THEN CRASHED TO THE GROUND. NO PREIMPACT PART FAILURE OR MALFUNCTION OF THE ACFT WAS FOUND, THOUGH IT WAS DESTROYED BY IMPACT & FIRE.