Mark Zuckerberg’s fortune has tumbled US$17.4 billion so far this year as Facebook Inc. faces fresh criticism over its treatment of critics and continues to grapple with the fallout from its response to Russian election meddling.

Shares of the social media giant fell 3 per cent Friday to US$139.53, the lowest since April 2017. Zuckerberg, 34, who recently was the world’s third-richest person, behind Jeff Bezos and Bill Gates, is now ranked sixth on the Bloomberg Billionaires Index.

Zuckerberg’s fortune, now at US$55.3 billion, has tumbled more than US$31 billion from its peak on July 25. Oracle Corp.’s Larry Ellison, is close behind at No. 7 with US$54.7 billion.

Zuckerberg faced renewed pressure Friday, with a group of Democratic senators demanding that he respond to news reports that the company used contractors to retaliate against critics of its privacy practices and efforts to thwart Russian propaganda on its network.