There would be hair, lots of blood and a dead deer right near by. I've seen some interesting things in the woods but never a nech shot animal that didn't bleed and bleed profusely. Think about it, when you process a deer what's in the neck? Tendons, arteries, spine and spinal cord, smaller secondary veins windpipe esophagus and I could go on. A neck shot is generally lethal, low percentage shot but lethal non the less. If you saw the hit you should be able to find hair, blood & fatty grissle.
If you've tracked the animal any distance at all and found none of these I'm still guessing you missed.

Did you shoot out of a tree? If so I'd search behind where the animal was when you shot. you should be able to find the arrow. If not you should have been able to see the arrow sticking out of the deers neck as it ran off. I'm not sure ewhat to tell you. I'd look again and see if you can't find evidence that points one way or the other.