high hits you often don't get much blood, even if you clipped the top of the lungs. I've also center punched both lungs on deer before and had it look like a muscle hit...Only a couple times, but you never know.
If you can't follow the blood trail, really stop and ask yourself where you think he was headed after the shot (based on both direction and knowledge of the land)? Try a couple probes in that direction, following trails. If you don't get lucky (when I can't find blood, I always try the slightly educated probes first, hoping to speed up recovery and get lucky), grid search the area (concentric circles are fine, too). You need to make each pass so close that you think you're wasting time covering the ground twice. Make sure you check close under any brush pile, fallen tree and in every ditch.
Regardless of if you have a drop of blood or not, a grid will always turn him up, so long as he is dead, you are thorough with grid and you cover a big enough area.
Good Luck!