Zoo keepers are worried that a four-month-old stolen penguin may die if he doesn't get the care he needs.
Toga, a rare Blackfoot penguin, was snatched from Amazon World on the Isle of Wight on Saturday evening.
Keepers say he's just a baby who needs to be with his mum and dad and will not take food from humans.
Karen Bright, manager at Amazon World, said: "If he is not found quickly he will die as he relies on his parents for food."
Toga, who is 18in (45cm) tall, was the first and only baby Blackfoot penguin to be born under the zoo's endangered species scheme.
He is not as cuddly as he looks and will bite when frightened. He needs a special diet with supplements and he also needs to be kept cool, with plenty of fresh water he can splash about in.
Blackfoot penguins are also known as Jackass penguins because they make a sound like a donkey braying.
There are about 150-200 of the rare and endangered breed in the UK.
Ms Bright added: "Toga will start to become very ill after about five days without food.
"We feed his parents marine fish containing salt tablets and vitamins, which they regurgitate and then feed to him."
A police spokesman said: "If you have knowledge of the whereabouts of Toga the penguin, ring Amazon World and zoo staff will come and collect him."