Two weeks later, Mr. Systrom had boiled down the app's mission to one lofty, if perhaps hokey, phrase: "to capture and share the world's moments." It was a rallying principle that Instagram could now sell to its staff, its users and, just as important, future advertisers.

As director of business operations, the 35-year-old Ms. White effectively is the new chief operating officer of Instagram, the point person charged with turning a billion-dollar acquisition that has never made a cent into a real business. Mr. Systrom, co-founder of Instagram, still makes the ultimate decisions, but it is Ms. White who is responsible for courting brand marketers and laying the foundation for advertising.

There are no ads on Instagram, but Ms. White said it should be ready to begin selling ads within the next year.

Her challenge is to figure out how to integrate marketing without jeopardizing Instagram's cool factor.

"We want to make money in the long term, but we don't have any short-term pressure," she said.

Since Mr. Systrom created the app in 2010, Instagram has focused on attracting users, wooing them with a clean design and a simple way to share photos with an artsy patina. Instagram said it has more than 150 million monthly active users, a gain of roughly 128 million since Facebook bought the app last year. At that pace, it swiftly is closing in on seven-year-old rival Twitter Inc., which announced it had "well over" 200 million active users in March.

The pairing of Ms. White and Mr. Systrom echoes another power duo on campus: Facebook CEO Mark Zuckerberg and operating chief Sheryl Sandberg, who has been a mentor to Ms. White.

A Vanderbilt University graduate with a minor in studio art, Ms. White, like Ms. Sandberg, began working for Google Inc. in 2001, where she was a salesperson for Google's AdWords products and, later, Google's overseas operation. In 2010 Ms. Sandberg wooed Ms. White to Facebook to put her in charge of sales and marketing for local products. Not all her campaigns took off, such as Deals, a local-deals service, that never moved beyond the test phase. In late 2011, she became the senior director of mobile partnerships, hammering out deals with wireless carriers and other mobile partners.

When Ms. White joined Instagram, the company didn't even have the outlines of a business. At the beginning of this year, it employed 32 people, largely focused on product, with no one handling customer service, no one on analytics and just one person working with the thousands of brands who had started using the service to promote themselves.

To get the basics in order, Ms. White reviewed every business function in the organization. It now employs 50 people, including two people working on analytics and four people to help manage relationships with brands.

Under Ms. White's direction, the team cataloged every major brand-marketer account on Instagram. Then she went to meet the companies. Last week she had meetings with Ford Motor Co., Williams-Sonoma Inc. and Coca-Cola Co.

After years without ads, Instagram's big risk is alienating its members—especially its large base of teen and young adults, who are coveted by marketers. Too much overt marketing could clutter the service, undermining one of its strongest selling points.

"Theoretically, [Instagram] could be making hundreds of millions of dollars today, but they would need a big sales force and they would risk polluting the environment," said Brian Wieser, an analyst at Pivotal Research Group.

Users have already pushed back. Instagram provoked a brief uprising last December when some members complained after a change in the app's terms of service implied that user content could be turned into ads. Ms. White said there are third-party services that brands can use today to get permission for access to user content but that Instagram is "not going to facilitate that."

It is also unclear if marketers will see the need to spend money on a service Instagram currently gives away free. Many, such as Nike Inc. and Lululemon Athletica Inc., are already active running free viral campaigns on Instagram. (Ms. White is on the board of Lululemon.) Meanwhile, Instagram has yet to set up a system to show advertisers the reach, or efficacy, of marketer content.

"Brands always demand metrics," said John Manoogian, co-founder of 140 Proof, a social-advertising service. "As it becomes a real advertising platform, they will be held to traditional standards, brands will want to see how these photos and videos tie back to their sales objectives."

On Friday, Levi Strauss & Co. kicked off a marketing campaign featuring Instagram. The campaign, a cross-country train ride, features a group of artists that will create music and art as they hit major cities. Cameras on the train automatically will upload photos and videos to Instagram. Instagram's team helped set up the technology, but Levi's didn't pay anything to the app company. Ms. White said such partnerships will help brands see the value of the service.

Julie Channing, the head of digital for Levi's, said Instagram is a "high priority platform."

"We now meet more regularly," she said.

What might paid Instagram ads look like? Ms. White's team is looking at the possibilities around the app's Discover feature, which promotes popular content, as well the search function, which allows users to look up images or themes. Ms. White said some retailers also are interested in ad products that will allow users to click on pictures of products that link to a retailer's own site. But she expressed reservations about such a system because many mobile websites need improvement.

Ms. White said she wanted to avoid repeating some of Facebook's earlier missteps with advertisers. She has regularly sought the advice of Facebook's top ad executives, including Ms. Sandberg; David Fischer, a vice president of business and marketing partnerships; and Carolyn Everson, a vice president of global marketing. Facebook "created a ton of different products and it got complicated," she said. The parent company has made strides in unwinding the complexity this year, she said. "I'm always looking at how to keep it simple."

Write to Evelyn M. Rusli at evelyn.rusli@wsj.com