Square Inc. shares plunged during trading Oct. 11, a day after the company announced CFO Sarah Friar was departing to join Nextdoor.com Inc. as CEO.

Friar has been largely regarded as the day-to-day supervisor of the financial technology company, which is led by Chairman, President and CEO Jack Dorsey, who also helms Twitter Inc. Friar was a leading force in Square's initial public offering in 2015 and has since overseen the company's expansion outside of the U.S. and move into the e-commerce business, Guggenheim Securities analyst Jeff Cantwell wrote in an Oct. 10 research report.

"Her departure leaves sizable shoes to fill for Square," Cantwell wrote.

After hitting an all-time high in September, Square's stock has since plunged approximately 30%. As of 11:49 a.m. ET, shares of Square were down 10.65% on the day to $69.20.

The rapid sell-off in Square's stock coincides with a marketwide rout as the S&P 500 has fallen 4.4% since Oct. 9.