I agree with others that the blood trail might be sparse. No exit on the "downhill" side of the body will restrict the blood trail a bunch. I am some what surprised that the arrow having gone in 18" was able to be pulled out as the deer ran off. But I suppose not impossible at all. I'd suggest starting where you first saw blood and mark what blood you can find with tiolet paper and see if you can get a general direction that the buck fled, keeping in mind where you last saw him. Once the blood trail is a goner, then about all that you can do is do a thorough grid search from there on. Get a buddy or two and cover at least 1/2 mile square if at all possible. Take your time and cover the ground very carefully examoining any brush piles, ravines , creeks and thickets closely. If he is not down inside that square, then you are probably out of luck finding him. If you have access to a blood trailing pooch, by all means get the dog in there and on the track. Be interesting to know if you find it.