SEA90FA028

During a wx briefing, the non-instrument rated canadian plt was advised that VFR flt was not recommended. However, he departed with a VFR flt plan & rcvd VFR flt following from ATC. While cruising at night at 3000 ft MSL, he was notified that radar contact was lost & to resume his own navigation. A freq change was approved & no there was no further communication with the acft. Subsequently, it collided with trees & crashed in mountainous terrain. Evidence of tree contact was found at an elevation of 2800 ft. the main wrechage came to rest on lower terrain about 1500 ft beyond & 1000 ft below the initial impact point. About 11 mi west at olympia (elev 206 ft), the 1950 PST wx was in part: 3000 ft ovc, vis 5 mi, wind fm 200 deg at 20 KTS. No preimpact part failure or malfunction was found.