I dont have any experience with fadeing puppy syndrome but was very interested to read a post on the thread Help with fadeing puppy page 2 of this section. Now Im not sure if this is what your pup has or whether hes not wanting to eat for other reasons but it might be worth you having a read of this thread. The lady speaks of Plasma transfusion which helped some of her litter

Oh gosh I do hope things pick up for the little one, you must be beside yourself with worry x