DETROIT (CNN) -- Nineteen-year-old James Johnson found a young pit bull puppy running up Seven Mile Road in Detroit this week. He took her in and named her Trina.

It's not the first stray dog Johnson has found on the streets of Motor City. Four years ago, he found an emaciated pit bull he named Campsite hiding beneath a trailer.

In America's biggest bankrupt city -- currently more than $18 billion in debt and home to 70,000-plus vacant structures -- there is another problem: Tens of thousands of stray dogs roam the streets.

As many of Detroit's residents struggle to get by, many of its dogs are left abandoned -- scavenging for food wherever they can find it.

The problem isn't a result of the city's bankruptcy filing. In fact, it's been a vicious cycle in this city for decades. As the economy sputtered in Detroit and manufacturing jobs disappeared, more dogs were abandoned. They're starving not just for food, but for affection.

"They're over-breeding. They're running the streets," says Kristen Huston from All About Animals Rescue, whose mission is keep dogs in their homes or to otherwise prevent them becoming homeless.

"A lot of people have lost their homes, lost their jobs and they just don't have the funds," she says. "They love their animals but it's very hard to feed their own kids and family."

Huston spends her days feeding stray dogs and canvassing neighborhoods to educate dog owners about the importance of spaying and neutering. She's part of the Pet for Life program, which provides free spay and neuter surgeries through a $50,000 grant from the Humane Society of the United States.

Ninety percent of the strays are pit bulls or pit mixes -- popular with residents to use as guard dogs, according to Harry Ward, who runs Detroit Animal Control. He and his team are responsible for responding to an overwhelming amount of calls about strays. Seventy percent of the strays they take in will be euthanized within a week if no owner comes forward, per state law, Ward says.

"I know that that is distasteful to a lot of people," he says, "but people need to know what the state law is on this and how this goes."

Four years ago, Ward had 15 animal control officers who would round up strays. Today, he has four -- a third of the staff he says he needs. Technically, Detroit Animal Control has a $1.6 million annual budget, but Ward says positions he needs filled have been tied up in red tape.

Emblematic of the city's financial woes, the metal letters that read "DETROIT ANIMAL CONTROL" on the front of Ward's headquarters were stolen to be sold as scrap metal.

Meanwhile, Detroit ranks sixth on the 2012 U.S. Postal Service list of cities with the most dog attacks on mail carriers. Donald Montgomery carries "Back Off Dog Repellant" on his delivery routes and says he uses it several times a month.

"Where there's a lot of vacancies, they [stray dogs] take shelter in the vacant houses...abandoned cars," explains Montgomery. "We just deliver with caution, take our time."

During a recent visit to the Michigan Humane Society, one stray dog after another was brought in for evaluation. Most looked like skeletons, shaking, with their tail beneath their legs. They were weighed, given shots and then fed. Each attacked the metal bowl filled with food, scarfing it down, making it clear it had likely been weeks since they saw their last meal.

"They're like disposable lighters. They don't seem to have any value to people. So they're left behind easily and abandoned and left to run stray," says Deborah MacDonald, the chief cruelty investigator for the Michigan Humane Society in Detroit.

MacDonald has been investigating cases of abused dogs for 25 years. Asked what she thinks the key problem is, she says, "Irresponsible pet ownership. They're disposable in people's minds. They don't vaccinate, they don't spay, they don't neuter."

Tom McPhee is determined to get to the root of the problem. He founded the World Animal Awareness Society and is on a mission to count all the stray dogs in Detroit. He says recent reports of 50,000 stray dogs in his city are inflated -- but says the problem is severe. McPhee acknowledges the vast array of problems facing Detroit but says the stray dog epidemic matters because, "This is like the balance of health in this community and so this greatly affects the balance of that health."

McPhee says the thousands of abandoned structures across Detroit are a big part of the problem -- providing shelter for strays.

"What's happening now is people are just quickly absorbing animals and then passing them on to other people -- there is no sense of guardianship or responsibility of having an animal. The basic think that needs to change is that people understand the responsibility of being a guardian for a dog."

But there are those trying desperately to keep their dogs even when they fall on hard times. Howard Fullerton says when he lost his home to foreclosure he had to leave his 9-year-old pit bull Coco behind as he moved into an apartment with relatives.

"She's been in our family for nine years, since she was 6 weeks old," he says.

Coco lives in the backyard of the home she used to share with Fullerton. That is, she will until the bank sells the house.

Fullerton comes back to feed Coco daily. He posted a sign on the garage door which reads: "Dog is not abandoned. Coming back."

"The heartbreaking part is when I come walk her and spend a little time with her and leave, she just cries and whines," he says.

On a routine run with Animal Control this week, CNN saw five stray pit bulls taken in within less than two hours. One was chained up in the backyard of a burnt-out, abandoned home. It's unclear how long the dog had been left without food, water or shelter. Another was a young black pit bill, so injured he could barely walk.

"This is one of those prime examples of a discarded animal," said animal control officer Malachi Jackson.

Jackson has seen a lot, too much, in his 19 years rounding up strays in Detroit.

"The problem is as bad as the economic problem I think. The whole society is pretty bad. People don't have jobs, they use animals to build revenue and protect their property. An animal is like a burglar alarm or a security guard for those people. Times are just tough."

Tough to say the least. And like so much else in Detroit, man's best friend is waiting to be rescued.

As for Trina, the pit bull puppy James Johnson found running stray, he says he plans to breed her for at least one litter of puppies. "I like puppies -- I ain't going to lie," Johnson says.

It's a choice, Kristen Huston says, that is understandable but contributes to the problem. A problem plaguing this city as it fights to get back on its feet.