As for finding them, First I just look for the little v's made in the sand. If that does not work, look for structure i.e. rocks or pier pilings. Also look for the channels in the sand or anything irregular in the shape of the sand. Last but not least, check different depths. Sometimes they are in 1-2 feet of water(thick). Whatever you do keep moving until you find them, that is usually where the fish are too.

As for digging them up, I use my hands and find plenty. I keep a crappy old fanny pack with me which works great for storage. Once I locate them I dig in with fingers spread open and "rake" around until one slips into my hand. I usually will only catch a dozen at a time, and go back for more when I need them.

As for hooking, I hook on one of the "rear quarter panels"of the shell only. This gives more action and they live longer. I heard that they will bleed to death if you hook them in a vital part, that might be the reason yours are dieing so fast. With this hooking method you need to make sure your crab does not dig in to the sand so give it a tug every ten seconds or so and you will feel the crab dislodging from the sand.