The 12-month-old pug Lola was being taken for a walk on Sunday night in Carlisle, in Perth's inner-east, when a white Pit Bull jumped out of a vehicle stopped at the lights.
Lola's owners claim the dog - described as either a pit bull or Staffordshire Pit Bull Terrier - launched a savage attack on the helpless pug before being whisked away by its owner.
'The Pit Bull latched on to Lola's neck and was lifting her up and ripping her apart,' Lola's owner Ellie McKay told 9 News.
Ms McKay and her fiancee Simon Warman pulled the larger dog away from Lola who was badly injured.
But in her distressed state, Lola ran away from her owners and directly into the path of an oncoming truck.
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.
"It was the worst experience of my entire life."
CCTV from a nearby liquor store shows the driver of the white vehicle chasing after his dog after the attack.
Ms McKay said the man gathered his dog and left the pair there screaming in despair.
"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."
The couple are pleading for the public's help to find the owner who is described as fair skinned, in his late 50s with grey hair and stubble, according to 9 News.