Jason was known to be naked and barefoot in a rough, hazardous and unforgiving environment with likely bleeding (a target rich situation for tracker dogs). YET, there is no usable scent trail, despite known bare skin on ground, but somehow he managed to successfully traverse to an unknown location and hide himself so effectively that years later, no trace has been found. Even though with every step, his injuries would increase and more and more blood would be lost. The Texas Monthly articles states that trackers using trained dogs began looking for a track the evening after Jason disappeared. The weather was cool and dry.
If we were talking about a missing woman under the same circumstances, all would say FOUL PLAY.