Simon Hooker, of Smelter Wood Road, Richmond, was in bed asleep in the early evening on Monday (February 22) when he heard voices outside his bedroom door.
He got up and found two masked men in his flat, who had entered after his girlfriend forgot to lock the door as she left in the daytime.
One of the men held a knife to his face, and the other stole four six-week-old puppies that Mr Hooker’s dog had given birth to.
Mr Hooker, 50, said: “I was so scared. I thought they were going to stab me.
"A man taller than me held a knife level to my face and said ‘stay back or you will get it’.
"He said if I did anything he would stab me in the face.
"I am in still in shock. I am heartbroken because the puppies are gone.
"I am not working at the moment due to illness. I live alone and I suffer from severe depression, suicidal thoughts and anxiety.
"I’ve got no support whatsoever and I am quite lonely to be honest. I love dogs and they are what keep me company and help with the depression. They get me out of the house.
“My dog, their mum, is getting old, so the puppies were for the future. One was going to go to my girlfriend and one to her daughter.
“They are too young to be taken. They have not been chipped or had their injections.
"I am worried sick about what could happen to them in the wrong hands. They have to surface somewhere and I need to get the word out so people can find them.”
Three male puppies and one female puppy were stolen. Their mother is a mastiff mix and their father a cane corso.
Two of the puppies are black and white and two are brindle. Their names are Tyson, Paddy, Ronnie and Rocksy.
One of the brindle puppies has dew claws on its back leg, making it easy to identify.
Mr Hooker is suspicious that the people who stole his dogs must have known about them.
"The thieves obviously knew what they were after when they came to my flat,” he said.
"What is odd is that my dog, their mother, did not bark. But because they just walked in through the open door she must have not seen it as a threat.”
South Yorkshire Police, including a CID team, are reviewing CCTV of the men visiting Mr Hooker’s flat, and are investigating the theft.
If you know anything about the incident you can contact police on 101, quoting reference number 0118-22/02/2021.
South Yorkshire Police recently said reported dog thefts had risen over the last few months.
Officer Paul Newman said: “Please be aware that a specific crime is on the increase in the Sheffield area.
“The crime is regarding the theft of dogs. All ages of dogs are being targeted that are being left outside shops and in some cases people have been approached and asked if they would ‘sell’ their dog."
Police say that while they are aware of lots of anecdotal claims of dog thefts like this, only a small number are reported, making it difficult to understand how widespread the problem is in Sheffield.