Shares of Facebook Inc fell 4 percent on Friday after Chief Executive Mark Zuckerberg announced changes to the platform's centerpiece News Feed that he said would hit user engagement in the near term.
Zuckerberg said on Thursday the company would change the filter for the News Feed to prioritize what friends and family share, while reducing the amount of non-advertising content from publishers and brands.
If the premarket declines in shares hold, Facebook stands to lose nearly $23 billion from its market capitalization on Friday as a result of the move.
Pivotal Research Group said its analysis of Nielsen's digital consumption rates showed that usage was already falling prior to Zuckerberg's announcement, although from very high levels.
"We can speculate that the concerns reflected in Zuckerberg's post may very well have been driving these declines," Pivotal's Brian Wieser wrote in a note.
The company has been criticized for algorithms that may have prioritized misleading news and misinformation in people's feeds, influencing the 2016 American presidential election as well as political discourse in many countries.
While, Facebook's advertising would be unaffected by the changes, the shift was likely to mean that the time people spend on Facebook and some measures of engagement would go down in the short term, Facebook said.
It may also have an impact on major suppliers of news and other content.
John Ridding, the chief executive of the Financial Times, warned on Friday that the domination of online advertising revenue by search and social media platforms was putting pressure on media firms.
"The FT welcomes moves to recognize and support trusted and reliable news and analysis. But a sustainable solution to the challenges of the new information ecosystem requires further measures," he said.
"In particular, a viable subscription model on platforms that enables publishers to build a direct relationship with readers and to manage the terms of access to their content."