Trying to find a misguided arrow shot from ground level can be a real chore. Since you've already tried a metal detector, that arrow may be a lost cause. What was the terrain like? Did you hear it strike anything on its way? I've seen long range practice arrows (launched from 80 yards) skip and stick in brush many yards back and above wasit level. You could try a yard rake, but it's kinda hard to say where it went not knowing the shot circumstances.