The Staffordshire bull terrier was found with a broken back in the middle of the road in A5104 near Treuddyn, Wales.
Shocked members of the public found the critically injured dog with a strangulation ligature cord around her neck at around 12pm on July 19.
Both her back legs were broken too.
The RSPCA said it is now leading a probe to try and find the thugs responsible.
“The dog was examined but unfortunately due to the severity of her injuries the vet decided that the kindest and only option was to put her to sleep”
RSPCA deputy chief inspector Phil Lewis said: “This dog was found in the middle of the road – possibly after being dumped by a vehicle – by two members of the public who then kindly took the dog to the veterinary surgery in Wrexham.
“The dog was examined but unfortunately due to the severity of her injuries the vet decided that the kindest and only option was to put her to sleep.
“We’re now appealing for information to try and find where this dog came from and what happened to her.”
He thanked the “kindness” of those who found the dog and helped end her “horrendous” suffering.
“It is just awful to think how this dog may have suffered,” he said.
“She wasn’t microchipped so we don’t know her name or have any owner details to help with our enquiries.
“We’d very much like to thank the two members of public for showing their kindness to this poor dog who sadly didn’t make it through this horrendous incident.”