A Perth couple is pleading for the public's help to find the owner of a dog that mauled their puppy, which started a chain of distressing events that led to its death.

Simon Warman, 23, and 24-year-old Ellie McKay were walking their 12-month-old pug Lola near the corner of Wright Street and Orrong Road, Carlisle, on Sunday night.

A large white dog jumped out of a white ute, that was stopped at the traffic lights.

"The dog latched on to Lola's neck and was lifting her up and ripping her apart," Ms McKay said.

Pug 'Lola' was attacked by a larger dog, then ran onto the road in distress. (Supplied)

She and her partner were eventually able to pull the big dog away, but Lola was badly injured.

Distressed, the pug made a run for it in to incoming traffic.

Mr Warman said he ran after her, only to watch her collide with a moving truck.

"I just collapsed near her body," he said.

"I don't think we will ever get over watching her die," Ms McKay added.

The traumatic ordeal unfolded on the corner of Wright Street and Orrong Road in the Perth suburb of Carlisle. (Google Maps)

"It was the worst experience of my entire life."

CCTV from a nearby liquor store shows the driver of the white ute leaving his car running at the lights, and running after his dog.

"He just shrugged and said ‘sorry about that’ and put the dog back in his car," Ms McKay said.

"He just drove off and left us there screaming."