Stewart was told by a veterinary clinic in New Zealand that unless he could afford $2,500 surgery for 5-month-old Buck, who was hit by a car, his pet would have to be put down.
Stewart asked to see Buck one last time - then grabbed the pup and ran.
"I just knew I had to get my dog back. He's like my brother," Stewart told TV One's "Closeup" program Wednesday. "They can't just kill him because I haven't got any money."
The family, which lives on welfare in the North Island city of Wanganui, offered to pay the veterinary clinic $3.50 a week, but the clinic declined.
After the "dognapping," the clinic and New Zealand's Society for the Prevention of Cruelty to Animals then threatened the teenager with prosecution for cruelty to an animal unless he got veterinary care for the dog, which was in considerable pain.
But once the story got out the SPCA was flooded with calls offering donations to pay for the surgery and save Buck's life.
A determined Stewart said later he would rather be put behind bars than see his dog put down. "I'll go to jail for my dog," he told TV One.