The brindle-toned dog weighed only a pitiful 34kg (74lb) when he should have been up to a healthy 100kg (220lb).
RSPCA inspectors have launched an investigation after the dog died despite the efforts of vets.
The adult male dog was found on Hamstead Hill in Handsworth Wood, Birmingham on Saturday by three passersby.
RSPCA inspector Mike Scargill, who is investigating how the dog was in such an emaciated state, said: “He was very thin and in a bad way.
“The vets did what they could do to help him but sadly he died on Saturday night.
“The dog was not microchipped and was not wearing a collar so we have no way of knowing where he came from.
“I am appealing for the public to help us find out more about the dog.
“I would be grateful if the three men who found the dog could please contact me.
“Due to the appalling body condition that the dog was found in, it is imperative that we find out more about where this poor dog came from and how he came to end up in this terrible way.”
The RSPCA has released a picture of the dog to help with its appeal.
Anyone with information or who recognises the dog should call the RSPCA in complete confidence on 0300 123 8018.