Evie Chadwick, 14, was walking her dog Teddy in Bluebell Woods near West Ardsley on January 11.
At around 4pm Teddy was attacked by another dog, believed to look like a lurcher or bull cross, and ran away in fear.
Evie frantically called her parents, who ran to the woods in search of Teddy. He was found 45 minutes later shivering and covered in blood - and was put down by vets that evening due to his unsurvivable injuries.
The family could not locate the owner of the other dog and have reported the attack to the police, in the hope of getting some answers to how Teddy suffered his fatal injuries.
Teddy, an 18-month-old Jack Russell and Lurcher cross, was Evie's birthday present last year.
"She's distraught," Evie's mum Jo told the Yorkshire Evening Post.
"She doesn’t want to come home because there’s all the reminders around the house, it feels empty.
“We need answers, we want to know why. Why so brutal? If the dog hasn’t done it before, then why this time?
“She’s so angry and she can’t move on until something happens."
West Yorkshire Police have launched an investigation into the attack on Teddy and the family hope to find information on the owner of the other dog.
Evie believes the man was wearing a green jacket, glasses and a wooly hat with drop down ear muffs.
Her dad, Robert, said: "When a dad receives a phone call from his daughter and she screams, 'help me, there's blood everywhere', it leaves a sickening that cannot be described.
"We would appreciate any help in finding the owner. A dog needs to be walked. Someone knows."
A spokesperson for West Yorkshire Police said: "We received a report of a dog being injured by another dog in West Ardsley on January 11 and subsequently having to be put down.
"Enquiries are ongoing into the incident."
Anyone with information is asked to contact officers via 101 quoting log 1404 of January 11 or online via www.westyorkshire.police.uk/101livechat.
Support the YEP and become a subscriber today. Enjoy unlimited access to local news and the latest on Leeds United. With a digital subscription, you'll see fewer ads, enjoy faster load times, and get access to exclusive newsletters and content. Click here to subscribe.