Two men have appeared in court in South Africa accused of stealing a penguin called "Buddy" from a marine park and releasing him into the sea, police said Friday.

Adrian Donian, 22, and Emile du Plessis, 24, made a brief appearance in Port Elizabeth magistrate's court Thursday on charges of theft and malicious damage to property.

Buddy, an endangered African black-footed penguin, was taken from Bayworld Oceanarium in Port Elizabeth in a nighttime raid last week, triggering international concern over his fate as he is likely to die in the wild.

He was wrapped in a shirt, bundled in a car and taken the short distance to the coast where he was released into the Indian Ocean.

The two men handed themselves into Humewood police station in the city on Thursday accompanied by their lawyer.

Bayworld manager Dylan Bailey this week told AFP that they had confessed to the crime and said it was a demonstration against animals being kept in captivity.

But Bailey said Buddy, three, would not survive in the sea as he cannot hunt or fend for himself.

"The two men were charged and immediately appeared in court the same day and released on warning," police spokeswoman Priscilla Naidu told AFP.

"The case was postponed for further investigation. They will appear again in a month's time."

- Separated from mate -

Buddy, who was born in captivity, has also been separated from his mate Frances at the marine park, and one of their two chicks has since died, the local Herald newspaper reported.

The newspaper said that the two suspects looked remorseful and were "too traumatised" to speak to the media after the court appearance where they were supported by family and friends.

Bayworld staff and local volunteers have been searching along the coast for Buddy in the slim hope of finding him alive.

He has an identification tag with the number 266 on his left flipper. He also has a microchip, but no tracker.

Buddy was discovered missing the day after the theft when he could not be found for his monthly health check.

Security camera footage showed the men entering the penguin enclosure and taking selfie photographs before stealing Buddy and later releasing him at the nearby Pollock Beach.

African black-footed penguins, also known as jackass penguins due to the braying noises they make, have been rated as endangered since 2010 after suffering from commercial fishing and shortage of prey.