A compass, clear sightlines to points of reference, and a paper map can work wonders for orientation.
It's quite possible his things are where they were left and they were missed behind an unrecognized rock in a boulder field. People rarely stop and really look deeply at the path they've taken. The return trip can look quite different (time of day, personal exhaustion, etc.). If you can keep necessary gear on you, it's best. But if you really need to leave something make it dead obvious to find and then a few steps simpler yet. Necessary gear in the context of potential wind and freezing rain includes a decent jacket.
If everyone had prepared for a group trip (a couple hours hiking in the mountains) don't be the one to take off on your own, and try to caution anyone who wants to.
I think trying to reach his hiking party is entirely reasonable. They know best the planned route for the day and where the hiker should be. "can you see/hear (peak/river/waterfall)?" "if your looking at the peak is the sun in front/behind/left/right" of you?" could help reorient someone or make it obvious they went down a wrong side. but there is a tremendous amount of personal responsibility you're taking going off alone in the wilderness.