Waffle, who is six months old, was taken while being walked by his owner in St Austell at 7am on Monday morning.
Devon and Cornwall Police said a man approached the owner and threatened her with what she believed was a knife.
A spokesman said: "The suspect is described as being around 5ft 8in tall, was wearing a black, hooded top and scarf and spoke with a foreign accent.
"Anyone with information is urged to call police on 101, or email [email protected], quoting log number 0116 231219."