Facebook (FB) - Get Report announced a new head for one of its most important divisions on Monday, just a week after its co-founders said they would be leaving the company.

Last Tuesday, Instagram co-founders Kevin Systrom and Mike Krieger abruptly announced they were leaving the Facebook-owned social media platform, one of Facebook's biggest growth engines. Shares slipped, but Facebook's search for a new leader of Instagram has ended quickly, with the naming of Adam Mosseri Monday, Oct. 1.

"We are thrilled to hand over the reins to a product leader with a strong design background and a focus on craft and simplicity -- as well as a deep understanding of the importance of community," Systrom and Krieger said in a statement.

Mosseri was most recently Instagram's head of product and previously ran Instagram's news feed. For the short time that Instagram was without a chief, Mosseri had been the favorite to land the position.

The departures at the top of Instagram were reportedly related to tension between the co-founders and Facebook, which was pushing for more aggressive monetization on the platform. That was likely the same dynamic that played out between Facebook and the Founder of What'sApp, another Facebook subsidiary, as WhatsApp founder Jan Koum quit in April this year.

On Monday afternoon after the appointment, Facebook shares were down 1.4% to 162.15. Facebook is now down about 10.4% this year.

Start, and end, your trading day right with TheStreet's 'Daily Snapshot' on your favorite smart-speaker. Learn more about TheStreet's market coverage for your trusted smart-speaker here.

Facebook is a holding in Jim Cramer's Action Alerts PLUS member club. Want to be alerted before Jim Cramer buys or sells FB? Learn more now.

To be a profitable investor and build long-term wealth, you need the right information and techniques. Join TheStreet Oct. 13, 2018, for a special investing event for sophisticated and active traders. Register for "Invest Like the Pros: Jim Cramer's Boot Camp for Investors" here.

Want to Buy Stocks for a 10% or Greater Discount? You can with certain so-called "closed-end" mutual funds - an often overlooked investment class. Click here to register for a free online video in which TheStreet's retirement expert Robert Powell and an all-star panel run down all you need to know.