The social media company made headlines several times last week after its chief executive returned to the office from paternity leave. Upon his return, Zuckerberg took swift action on two major conflicts facing Facebook: a lawsuit over a proposed new class of shares and a probe into election advertisements.
Facebook settled the lawsuit by abandoning the proposed new class of shares, which would have included no voting rights and made it easier for Zuckerberg to maintain voting control over the company even as he cashed out his shares. The suing shareholders felt it was a bad idea to "separate economic interest from voting control," Stuart Grant, an attorney for Facebook shareholders, told CNBC on Monday.
Following the settlement, Zuckerberg said he would sell between 35 million and 75 million shares in the company over the next 18 months to support his other company, the Chan Zuckerberg Initiative, which invests in technology to address social issues.
Some investors consider high levels of stock ownership from insiders — like the CEO — as a sign that management has confidence in the company's future prospects.
The news of Zuckerberg's share sales came after he waded publicly into the political sphere earlier in the week. Zuckerberg said he instructed his staff on Thursday morning to provide Congress with 3,000 ads believed to be from Russian profiles, in an effort to assess "what happened in the 2016 election."
Some congressional investigators saw Russian activity on Facebook as key to understanding the extent of Moscow's influence on the election. Former President Barack Obama was also reportedly concerned.
The headlines around Zuckerberg cast a shadow on some of Facebook's good news: Instagram said Monday that it's added another 100 million monthly users.
"I do think investors are worried about regulatory scrutiny, and a lack of support from the White House — I am," Nancy Tengler, chief investment officer at Heartland Financial, told CNBC's "Closing Bell" on Monday.
Tengler said that Heartland has large stakes in Facebook, Google and Apple shares, but has been selling them.
"It feels a little bit like Microsoft in the '90s," Tengler said. "I think investors are kind of rethinking, 'What is this going to mean?'"
Facebook's move lower also came as the technology sector, as a whole, traded lower. The S&P 500 information technology sector closed 1.4 percent lower, and the tech-heavy Nasdaq ended the day down about 0.9 percent.
But Facebook shares traded at a volume more than 3 times higher than the average over the past 30 days.
"It's a correction," Tengler said. "Not a sell-off."
— CNBC's Jacob Pramuk and Michelle Castillo contributed to this report.