It sounds like you are doing everthing right. Id say find the thickest, nastiest stuff you can find and get in there. Most likely he is in there if he isn't next to the creek or near any other water source. We've found more than one buck in spring in stuff you can barely crawl through. When we used to rabbit hunt public land every december you could always count on finding at least one deer in the thick briars and thorns. If you checked everywhere else, I'd try to pick out the nastiest stuff within 500 yards and grid search that. Good Luck, we've all been there!