Get back out there at daylight and continue. If you can't find anymore blood, start a grid type search. The land dictates how thoroughly you need to search. If it's thick you might need to walk through every couple of feet.
A few things to consider:
-A little bit of blood goes a long way. Might look like buckets to us. But it really isn't.
-a wounded deer will usually take an easier path if given the option. Ex: uphill vs downhill.
-they will find some thick stuff to die in
-they can hide in a small area. Don't over look anything. It might be a clump of thick grass. A tree branch, a ditch, underneath farm equipment, they will pull themselves up into a hiding spot and you'll wonder "how'd a deer even get in there?"
-a wounded deer can cover allot of ground. I've seen deer make it a long way without a heart. Especially if they take off running, they can cover distance.
-when scanning and searching look for parts of a deer, not necessarily a whole deer. Try to get your eyes to pick up a flash of white or brown, horizontal line of it's back laying down, curve of an antler, a leg sticking out from under cover, etc. You're more likely to catch one of these things with your eyes than to just see the entire deer.
-it takes allot of time to search properly. But you owe it the deer. Especially in this case because you know you have a hit, and probably a pretty decent hit too.
-persistence: keep at it.
-Jake