It's looking less 'presumed' and more likely definitely downed. According to local news media updates, the CAP search crews were homing in on an Emergency Locator Transmitter in the vicinity received by both ground crews and the two blackhawk helicopters dispatched today to assist in the search efforts.
As of right now, it's been almost exactly 26 hours since the flight transponder telemetry was lost. I'm not sure how cold it was there (a ways south of Denver) last night, but here at 8700ft in the foothills, it was -8'F at 8am. The plane disappeared over terrain that ranges from 9-12.7K ft elevation while the region was experiencing in a snow storm. Snow accumulation likely compounded the difficulty of the search, already over mountainous and undeveloped terrain.