I always prefer fresh over frozen but at times you deal with what you got. I've had some success with blood worms, squid, and shrimp. However, if I'm using shrimp, I won't use it without squid. Slide the shrimp up the hook and attach a sliver of squid, hooked no more than one or two times, about 1/2 inch wide at the hood to a point and the end of the tail about 2 or 3 inches long. Don't let it sit. Cast it out and bounce it along the bottom as your retrieving.
My favorite thing to use for flounder is a small 1/8 oz jig head with white skirt hair. They come in green pink or white heads. Different colors work on different day and conditions as usual. Tip it with squid as described above. You will find that casting such a light jig head difficult so I use the following rig. Take 30lb test or so, cut it about 3 ft long. About 1 foot above the end tie a figure 8 knot that leaves a loop about 6 inches long. Tie another knot in the middle of the loop and then attach a 2 oz bottom weight (not a surf weight) just by looping it on. Then attach the jig to the end. Cast this out as far as you can and bounce it off the bottom as you retrieve. The weight kicks stuff up like a fish picking through the bottom stuff and will draw attention. The jig is the trailer the will draw the strike.
Let me know if this helps and you can follow how to make the rig. If your having trouble, I will post pics, step by step.
Update: It's not a figure eight knot, my bad. It's a dropper loop. Make this knot with a loop about 6 inches long and then tie a simple knot in the middle of the loop. ie 3" away from the drop loop and three inches away from the end of the loop. then attach the sinker.
http://www.animatedknots.com/dropper...matedknots.com
Good luck