Shares of Trump Media tumbled after former President Donald J. Trump, the company’s largest investor and primary user of its Truth Social platform, was found guilty of 34 felony counts of falsifying business records to cover up a sex scandal.

Trump Media shares were about 5 percent lower in premarket trading on Friday. The stock began falling immediately after the verdict in Mr. Trump’s trial in Manhattan was announced on Thursday, which came after the stock market had closed. Shares sank by as much as 14 percent at one point.

The company’s stock is typically volatile, so such large moves are not unusual, especially after the official close of regular trading, when low trading volumes can accentuate price swings. Still, it marked one of the few ways in which investors could react to the trial in real time, with the price move closely tied to news of the verdict.

Trump Media remains richly valued relative to the size of its business. Even after its recent decline, the company is worth more than $8.5 billion in market value. Mr. Trump owns about two-thirds of the company’s shares, a stake worth about $5.5 billion. The stock has become his main source of wealth since Trump Media make its market debut in March, but he cannot sell or borrow against the shares until September.

Trump Media has reported steep losses and modest revenue, which derives from advertising on Truth Social. In the first quarter of this year, the company recorded an operating loss of $12.1 million and $770,000 in revenue, a 30 percent drop in sales from the same period a year ago.

On Truth Social, which has become Mr. Trump’s personal megaphone to rail against judges, prosecutors and critics, many users rallied to his defense. The roughly seven million registered users of Truth Social are some of Mr. Trump’s most ardent supporters and many are also investors in Trump Media, which partly explains the sky-high valuation of the company’s shares.

On Friday morning. some of the trending topics of discussion on Truth Social were: “Trump2024,” “MAGA,” and “IStandwithTrump.”

Some Truth Social users put up posts with an upside down American flag, a possible reference to the controversy surrounding conservative Supreme Court Justice Samuel A. Alito Jr. An upside down flag is recognized as a sign of distress and some deniers of Mr. Trump’s 2020 election defeat had adopted it as a symbol of their belief. The New York Times reported that Mr. Alito’s wife had flown an upside down American flag outside of one of their homes in January 2021.

Mr. Trump’s presidential campaign immediately began to fundraise off the guilty verdict and some of those ads appeared on Truth Social. Several described Mr. Trump as a “political prisoner.”

Regulatory filings for Trump Media long have warned investors about the risk of Mr. Trump being convicted in one of the four criminal cases against in him state and federal courts. A recent filing said, “an adverse outcome in one or more of the ongoing legal proceedings in which President Donald J. Trump is involved could negatively impact” the company and the Truth Social platform.