By Jeff Rossen and Avni Patel, TODAY

(NBC) - Police say criminals are finding lost dogs and, instead of returning them, are selling them for a quick buck. It's a heartless new crime called "pet flipping" — and police fear it's growing.

Case in point: This summer, Leisa Waggoner's dog Rosie, a cute and feisty schnauzer, got lost on the streets of Indianapolis. Desperate, Waggoner posted flyers all over the neighborhood. When she went a lost dog website the next day, she got great news: Rosie had been found. But there was a twist: A con artist , posing as Rosie's owner, had already claimed the dog.

"She knew it wasn't her dog, but she claimed her," Waggoner said. "And next thing we knew, she'd listed her for sale on Craigslist," for $50.

At least 10 such cases of "pet flipping" — crooks trying to cash in on lost pets — have been reported in Indianapolis this year alone. Police say crooks can make anywhere from $50 to $1000 on one lost pet, depending on the breed.

Officer Theresa Redmon of the Indianapolis Metropolitan Police Department explained, "Sometimes they'll just find a missing pet; sometimes they'll answer a found ad and then they claim to be the owner of that pet. Or sometimes they'll just steal it right out of your yard."

And it can get even worse. Waggoner said that when she tracked down the woman trying to pawn Rosie, the thief tried to extort her. "She texted us and said that if we gave her a $250 reward, that she'd give our dog back to us."

Waggoner called police, who arrested the woman, Jennifer Dodd, who pled guilty to felony theft. Dodd told TODAY she did it for cash to buy diapers for her kids.

"I'm a single mom, I have fraternal twins on the way and I have a 1-year-old, and you know, the economy's hard and stuff nowadays," Dodd said.

But Waggoner said there is no excuse for stealing a member of her family for money. "It is awful that people would put other people through that kind of agony," she said.

To avoid becoming a victim of pet flipping, police advise that you not leave your pet unattended, even in your own yard. If your pet goes missing, check the pets section of Craigslist to see if someone is trying to sell it. And finally, get your pets microchipped: If someone finds your dog, it's an easy way to prove you own it. You can get it done at your local vet.