A beloved pooch was dognapped from outside a Williamsburg supermarket Monday night — with surveillance cameras capturing the moment a cruel thief snatched him by the collar and dragged him away.

Heartbroken film student Bre Kelly, 21, told The Post that she and her elderly border terrier mix Theo, 10, are regulars at the Green Corner Fish & Farmers Market — with people even giving the scrappy pup treats as he waited outside each week.

But when Kelly emerged from the grocery store at Humboldt Street and Flushing Avenue around 9 p.m. Monday, Theo was gone.

“I couldn’t breathe, and I also thought that I was imagining it. We frequent the neighborhood, and I walk around the neighborhood all the time,” Kelly said of the nightmare. “He’s small, he’s slightly hard of hearing, he’s got arthritis, he’s never run away, he has severe anxiety disorder from when we rescued him. He comes with me everywhere.”

After a frantic search, Kelly called police, who pulled up surveillance footage from cameras outside the grocery store.

The clip shows two men loitering outside — one of them appearing to keep a lookout as the other grabs Theo by the neck, dragging him and carrying him away.

“It was difficult for me to keep looking at the footage, and I just don’t really understand why you would steal a dog? He’s not an item,” Kelly said.

The NYU student and her father spent all of Tuesday morning posting 200 lost-dog flyers. They are offering a “large cash reward” for Theo’s safe return — no questions asked, a flyer states.

Dad Tom Kelly, 55, said the pair were “inseparable” after his daughter adopted Theo in 2009.

“This person doesn’t know the relationship they have,” he said of the dognapper. “She loves that dog more than anything. That dog would walk off a cliff for her. She would give her right arm for him. It’s crazy. I can’t believe it.”

Police have no leads but locals reportedly told Kelly they believed the two men lived in the neighborhood.

“I’m not worried about why they took him or pressing charges or anything,” she said. “I just want my dog back and I’ll do whatever it takes to work with them to make sure he’s safe.”