well welcome to the site, and sounds to me like a low belly shot, issue with shots like this can be from a grazing shot, to a larger wound that just got plugged up with intestines and won't maybe bleed much if at all
if you have access to a tracking dog, that would be the best idea I can think of, minus the grid search
there are a lot more folks out there with tracking dogs than ever, going to a few of the major web sites for them can many times find you one near you, that is if legal in your state/hunting area!
some charge a fee, if they have to travel far, or just charge no matter what, but many also do it for free, if there trying to get experience on there dogs, so its worth looking into
do a web search, never know other wise, your going to be doing a grid search and even then it can be iffy, a dog can be a HUGE help in cases like this

I wish you luck
and remember bad hits happen, it sucks for sure , but they do happen, just do your best and never know!
Please update how it goes!