Susan Smith was walking her West Highland Terrier cross Cooper in Dalton, near Thirsk, when a man leapt out of a van and tried to grab the dog’s lead.
Mrs Smith, 46, kicked the attacker and two-year-old Cooper slipped his lead before running off. He was later re-united with his owner after being found safe in a nearby field.
North Yorkshire Police detectives have received no other reports of similar incidents but say they are aware of rumours that dogs are being stolen and sold locally.
They have urged dog-owners to call the police if they spot anything amiss and to take precautions to make it harder for potential thieves.
Detective Constable Steve Harris of Northallerton CID said: “I am aware on Facebook there are rumours going round about people selling dogs, it is a common belief in the Thirsk area that people are doing it. There are rumours of people coming round in vans and taking dogs but this is the only reported case.”
The incident in Dalton was at 12.50pm on Thursday, when Mrs Smith was walking Cooper near The Oaks. A man got out of a blue van with dirty rear doors and muddy wheels and told Mrs Smith to give him the dog. She kicked him, allowing Cooper to escape, but suffered a cut wrist.
The attacker was in his mid 30s with mousy brown hair and had an Eastern European accent. He wore muddy lace-up boots, blue jeans and a blue parka style coat with fur around the hood.
A second man seen driving the van, which drove off towards the Jolly Farmer pub, had dark hair and a dark complexion.
Mrs Smith said she believed the men may have tried to steal Cooper because they thought he was a pedigree dog, as a pedigree West Highland Terrier can fetch £500.
She said: “I have heard that people are talking about this on Facebook and they are quite scared. My neighbour has heard of a dog being taken. It is frightening.”
Anyone with information should call North Yorkshire Police on 101, select option 2 and ask for Northallerton CID.
Police say dog owners can take precautionary measures to stop their pet being stolen, including microchipping, making sure the dog wears a collar and keeping it on a lead.
Breeders are urged to be careful who they invite into their home to view puppies for sale and limit the number of visitors at any one time.
In West Yorkshire, police are appealing for information about an unrelated incident where a dog was stolen in Bradford.
The Staffordshire Bull Terrier puppy was taken from Bradford Interchange at around 2pm on Thursday, 27 November.
The puppy is called Zeus and is light brown in colour with distinctive white markings. Anyone with information should contact DC 2432 Birch at Bradford District CID on 101 or Crimestoppers on 0800 555111.