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As Facebook (FB - Get Report)  embarks on a new chapter focused on privacy messaging, CEO Mark Zuckerberg announced Thursday after the close that Chief Product Officer Chris Cox will not be a part of this transition. 

Cox's departure was announced in a blog post from Zuckerberg in which he reiterated the social media company's new focus on being a "privacy-focused social platform."

"At this point, we have made real progress on many issues and we have a clear plan for our apps, centered around making private messaging, stories and groups the foundation of the experience, including enabling encryption and interoperability across our services," Zuckerberg wrote. "As we embark on this next major chapter, Chris has decided now is the time to step back from leading these teams."

Facebook shares were falling 1.9% to $166.99 after hours Thursday on the news, after falling 1.9% during the day's trading.

Cox has played an integral role in Facebook's development, starting as an engineer on the  original News Feed, building its first HR teams, leading product and design teams, running the Facebook app, and most recently determining strategy for the company's family of apps, according to Zuckerberg's post.

In addition to Cox's departure, Zuckerberg also announced that Chris Daniels, who ran the company's business development team and WhatsApp, will be leaving the company. Daniels will be succeeded by Will Cathcart as the head of WhatsApp. 

Zuckerberg also announced that Fidji Simo will be the new head of the Facebook app as part of a restructuring that will see the company's CEO take a more direct role in the wake of Cox's resignation. 

"I do not plan on immediately appointing anyone to fill Chris's role in the near term. Instead, the leaders of Facebook (Fidji Simo), Instagram (Adam Mosseri), Messenger (Stan Chudnovsky), and WhatsApp (Will Cathcart) will report directly to me, and our Chief Marketing Officer (Antonio Lucio) will report directly to Sheryl [Sandberg]," Zuckerberg said. 

Facebook is a key holding in Jim Cramer's Action Alerts PLUS charitable trust. 

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