Symantec shed a third of its value Friday in the stock's worst day in 17 years.
Shares fell 33 percent percent to close at $19.52. At one point, shares fell as low as $18.85 — levels not seen since June 2016.
The cybersecurity company, which makes Norton anti-virus software, said Thursday it has launched an internal audit in response to concerns from a former employee.
The company did not elaborate, saying only that the investigation was not security-related.
"The investigation is in its early stages and the Company cannot predict the duration or outcome of the investigation," Symantec said in a statement.
A source familiar with the matter told Reuters it was separate from another investigation launched in November into the possible violations of federal securities laws in relation to its executive compensation awards.
After the announcement, at least eight third-party investor groups said they launched investigations into the company.
Rosen Law Firm, which represents one of the investor groups, said it is investigating whether Symantec "may have issued materially misleading business information to the investing public."
In addition, at least nine Wall Street analysts lowered their price targets for the stock.
Symantec executives declined to take questions from analysts during the company's earnings call. Symantec beat Wall Street estimates when it reported fourth quarter and full-year results Thursday.
"The fog created by an internal investigation of the company led by the audit committee of the board, with no semblance of detail provided to investors, overshadows everything else in Thursday's Q4 and FY 2018 earnings," BTIG analysts wrote in a note.
Friday's plunge is the company's second worst trading day since going public in 1989. It slashed $6 billion off the company's market value, according to FactSet estimates of shares outstanding.
As of Friday's close, the stock is now down 37 percent in the 12-month period and is more than 40 percent off its 52-week high.
—CNBC's Ari Levy and Reuters contributed to this report.