In a new ad for PETA, shown first on PEOPLE.com, Stewart poses with his rescue poodle Pookie, and urges people to adopt animals from shelters and rescue organizations instead of buying them from pet stores.
In a behind-the-scenes video for the campaign, the 17-year-old recalls how he rescued Pookie, once abused, from a man who couldn't care for her anymore. Stewart marvels at her transformation from scared pup to happy and affectionate companion.
"I can hold her like a baby," he says. "She likes putting her legs around me, not off to one side. If you guys are interested in getting any kind of animal, definitely go and adopt an animal, don't go to a pet store where they just sell their animals."
Stewart goes on to say how saddened he was when he watched a video of the annual baby seal hunt in Canada with his costar Kellan Lutz. "They have feelings," he says of animals. "My dog loves me – I know that."