She grabbed his car keys, ran out the door and drove off.
Mr Hayes reported the incident to police, who later told him the car had been crashed and written off.
He can't afford insurance and has no money for another car so is now holed up in his flat and can no longer visit his wife's grave.
Mr Hayes said he had wanted to give up on life after this latest blow.
After reading about his ordeal in The Daily Post, people started collecting money to buy him a new car.
Rotorua's What's Cooking Lunch Bar staff put a copy of the story on the wall and within 90 minutes had collected $100.
Owner of the Vaughan Rd cafe, Johanne Fell, said reading about Mr Hayes' plight had not only made her angry but also sad about what could have happened to the thieves to make them show such disrespect.
"We just want to restore in his mind that there are people who care."
Mrs Fell stuck the story up about 11.30am yesterday and grabbed the "closest vase" for people to put money in.
She planned to continue the collection for a few days and raise as much money as they could to buy Mr Hayes a car.
"We've had people give $10."
Mrs Fell challenged other Rotorua businesses to collect money.
Rotorua women Rach Bennett and Michelle Hope have set up the event Gift for Gav on the Facebook page Rotorua Buy Sell & Swap to raise money so Mr Hayes can buy a new car. "I think it might help show him that there are nice people out there," Ms Bennett said.
Rental firm Rotorua Rent-a-dent had offered to deliver a car to Mr Hayes to use free for a week.
Matthew Leef contacted The Daily Post and offered to drive for Mr Hayes. "I'm absolutely ashamed by the behaviour of these teens and I'd like the chance to be a good person and hopefully restore his faith in humanity."
Mr Hayes' neighbour said someone had contacted Mr Hayes and offered to take him to Taumarunui this weekend. Mr Hayes said he was overwhelmed by what people were doing for him.
"That's nice ... I didn't expect all that. That's marvellous."