The idea seems simple: Take someone's picture, ask them a few questions, then post the photo and the interview online.

That's how bond trader turned photographer Brandon Stanton's "Humans of New York" blog became a social media sensation around the world.

"I was at an end of a two-year period where I thought about nothing but money and I had nothing to show for it," he said in an interview with CNBC.

Read MoreFacebook's big move into your work communication

After being laid off during the onset of the 2008 global financial crisis, the Georgia native changed his mind about his career path. He ignored money for a while in order to build a life that was focused on something he loved.

With no formal training in photography, his newfound professional pursuit and passion led him to a place he had never been to before—New York City.

"I was very poor for about two years," Stanton said. "I collected about $16,000 from unemployment. I slept on an air mattress and didn't eat well."

One of the reasons he came to New York City was because it's one of the very few cities where he could walk around all day and take pictures without needing a car.

"New York is the first stop for so many people moving to America," Stanton said.

That led to the 2010 creation of the photo blog, which features random people in the city and tells their personal stories. In four years, it's become enormously popular with more than 11 million likes on Facebook, 2.2 million followers on Instagram and nearly 200,000 followers on Twitter.

Released in 2013, Stanton's "Humans of New York" book of portraits rose to No. 1 on The New York Times best-seller list. And in October, his second book— "Little Humans"— was released. The children's book combines an original narrative with some of Stanton's favorite photos of kids from the blog.

Read MoreSocial wars heat up

He says the online explosion didn't occur until he started including stories about the thousands of strangers he met, which he got after he took their pictures.

"Social media is a superimposing place where people are usually bragging," Stanton said. "On 'Humans' [the blog] people resonated with pictures of folks who often have the same burdens being honest about expressing their weaknesses and strengths."

This past summer, the United Nations decided to make "Humans" global, sending Stanton on a two-month trip to through swaths of the Middle East, Africa and Asia, among other countries. The goal of Stanton's world tour was to help the U.N. highlight countries affected by problems they are trying to remedy.

He says the universal thread that all humans share is their ambitions and hopes. In poorer countries, there are vastly different means to achieve those ambitions. "Being a doctor, lawyer in war torn countries isn't easy when the infrastructure isn't there," Stanton said.

"The money, the food and education is not always accessible to achieve those dreams."

Nevertheless, Stanton's work and inspiration is still in the city that never sleeps. "I've taken pictures in at least 14 countries and nowhere have people told me 'no' more than New York City."

He says his early days as a bond trader contributed to how he manages his photography career.

"My two biggest lessons learned as a trader are take risks and get comfortable with taking losses and setbacks to help move you forward."

"On the Money" airs on CNBC Sundays at 7:30 pm, or check listings for airtimes in local markets.