SAN FRANCISCO — Unhappy with Facebook’s first financial report as a public company Thursday, investors fled the stock in droves even as Mark Zuckerberg, the company’s chief executive, extolled its growth prospects to industry analysts.

The disillusionment of investors was clear in after-hours trading, and when the market opened on Friday the depth of the disappointment was even more pronounced. Shortly before 11 a.m., the stock was down 14 percent, to slightly under $23 a share, a new low. That came on top of an 8 percent decline in regular trading on Thursday, even before the earnings announcement, on the chill from weak earnings from the social gaming creator Zynga, a major Facebook partner.

Since going public two months ago at $38 a share, Facebook has seen its stock lose 40 percent of its value.

Mr. Zuckerberg has rarely spoken publicly about the company he built in his dorm room eight years ago. But nothing he and his lieutenants said Thursday about their plans to make money by advertising to Facebook users seemed to reassure investors.