What’s white and black and has people fawning all over? Meet Siku, a polar bear cub born in captivity in Denmark.

The cute cub is being reared by handlers at the  Scandinavian Wildlife Park because its mother isn’t producing the milk to feed him. Since his birth last month, Siku has become a Web star. He has his own page on the Scandinavian Wildlife Park website and he’s even on Facebook.

Park director Frank Vigh-Larsen says he's stunned by the cub's rapid transformation into an Internet sensation.

Video footage posted on YouTube of Siku bottle-feeding, rolling around and snoozing has been viewed more than 2 million times in six days, he told CNN, and the cub gained thousands of friends on Facebook within the space of a few hours.

As of Wednesday, at 36 days old, Siku has just opened his eyes and weighs in at 4.2 kilograms (9.2 pounds), more than five times his initial weight, his handler said.

"He's just a little solid cannonball," Vigh-Larsen said. "He's doing well."

Such growth is a testament to the dedicated care Siku is receiving. For the first three weeks, Vigh-Larsen fed the cub every two hours - and still feeds him every three hours, meaning the keeper gets little sleep.

In the new year, two other wildlife keepers will start to care for him, too, in shifts, making sure the cub is never alone during the first 12 months of his life.

Siku's popularity comes at a time when the plight of polar bears is at its peak. Corporate giant Coca-Cola recently launched a campaign in conjunction with the World Wildlife Fund to raise awareness about arctic conditions that threaten polar bears.

Siku, which means “sea ice” in Greenlandic, an Eskimo language spoken in Greenland, is thriving under a bottle-feeding program instituted by the park’s keepers.

"Siku is going to be an ambassador for polar bears, for global warming," Vigh-Larsen said.

Vigh-Larsen draws a contrast with the last polar bear cub to become an Internet star, Germany's Knut. That bear died suddenly at age 4 last March at Zoo Berlin, to the sorrow of many worldwide who had followed the cub's progress after he was abandoned by his mother and hand-raised by a zookeeper.

The case of Knut was a disaster, Vigh-Larsen said, "because he was only ever used for selling tickets and teddy bears."

Siku will have a different mission, he says: using his cuteness to persuade people to listen to warnings about climate change and take steps to protect their planet.

It could prove a powerful weapon. The cub has already appeared on front pages of newspapers around the world and graced international TV news bulletins.

New pictures will be posted on the Wildlife Park's website Thursday, Vigh-Larsen said, with the pictures likely to win him even more fans.

Scientists believe there could be as few as 25,000 polar bears left in the world, according to Polar Bears International, a conservation group. The animals are only found in five nations, the United States (Alaska), Russia, Norway, Canada and Greenland, the group said.

In 2008, the U.S. Fish and Wildlife Service listed the polar bear as threatened under the Endangered Species Act.

CNN's Laura Smith-Spark contributed to this report.