When Sean Posner’s 7-year-old dog, Moose, was put to sleep in October 2011 after suffering from bone cancer, the Massapequa boy decided to honor his furry friend by giving back in his honor.

“I loved this dog,” Sean said. “We were very close.”

So Sean, then 11, gathered Moose’s toys and blankets, and encouraged his friends and family to bring new or gently used pet supplies to the big Halloween bash his parents were hosting later that month. He planned to donate it all to a local animal shelter.

“There were well over 100 people coming, so I thought if they each bring one or two things it would be a lot of stuff,” Sean, now 14, said.

But when most guests showed up to the party empty-handed, Sean said he had to take his cause to a broader audience.

“I was very mad, so I set out, going around town and putting posters up about a drive,” he said.

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Within weeks, he had collected more than $1,000 worth of donations, which he dropped off that December at The Little Shelter in Huntington. In return, the shelter presented him with a plaque bearing Moose’s name.

“I’d never done much charity work before and that was the best feeling I’ve ever had,” Sean recalled.

On the way home from the drop-off, Sean said he turned to his mother, Melanie Posner, and asked, “Why can’t all kids adopt a shelter?” That night — with help from his mom — he launched the Kids Adopt a Shelter Facebook page. When he awoke the next morning, he had more than 1,000 fans. Today that number has swelled to just over 13,000.

The charity, which is in the final stages of officially becoming a 501(c)(3), has spawned 26 chapters across the country. In 2013 alone, it assisted kids in adopting more than 70 animal shelters by giving them tools and guidance to hold collection drives and solicit sponsors. Petco has also become a big supporter.

Sean said he hopes to close out 2014 with 100 shelter “adoptions.”  

The charity is also helping to facilitate actual adoptions, getting animals out of shelters and into homes For the last two years, the group has held an annual fashion show outside the Petco in Massapequa, where adoptable dogs dressed in clothing walked the runway.  

After they were done “modeling,” many of the dogs — 15 in 2013 and 26 in 2014 — found homes. Included in that number was a pit bull named Kacy who had spent nearly three years in the Town of Hempstead Animal Shelter, Melanie Posner said.

“If you see a big pit bull in a cage all by himself, he’s probably not the happiest dog, he’s barking, and you’re not going to think he’s the sweetest dog,” Sean said. “When you see him walking around in an outfit that makes him look cute you are going to see he’s a sweet dog.”

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Sean, an actor whose stage name is Sean Martin, has appeared in movies including “The Dark Knight Rises” and “Tower Heist” and has recruited actor Larry Romano (Ritchie from “The King of Queens”) to help with his charity. The next step, Sean said, is working with elected officials to reform the penalties for animal abusers and backyard breeders in New York State.

Sean’s family now has four dogs — all rescues — but he said Moose will always hold a special place in his heart.

“That dog loved everyone,” he said. “He would want other dogs to be happy, because he was a very good guy.”