Facebook’s debut on Wall Street last week may have been so-so. But on Monday, it officially flopped.

Shares dropped 11 percent from the original starting price.

For the social-networking company, which declares that its mission is to “make the world more open and connected,” the investors had a pointed response: Put up or shut up.

“We’re very bullish on Facebook, but the share price just wasn’t justified,” said Rick Summer, an analyst at Morningstar. “It was overvalued.”

Exactly what a share of a new company is worth is often a matter of much dispute, and Facebook’s assessment of its own worth grew considerably as the initial public offering approached.

The company initially said the appropriate range was $28 to $35. Then last week, as anticipation grew, it raised the range, $34 to $38.

On Friday, its first day of public trading, the company started selling stock at the high end of the second range, or $38.

Despite the hoopla that came with one of the largest offerings of U.S. stock, the reaction from investors was tepid. Share prices would have plunged immediately if not for the intervention of Morgan Stanley and at least one of the other banks underwriting the company’s public offering. They bought stock to prop up the price, and it closed Friday just above $38.

But at the opening bell Monday, the Facebook share price dropped and closed at $34. That one day of trading wiped out about $11 billion of the company’s value, at least on paper. Chief executive Mark Zuckerberg personally lost about $2 billion Monday.

The drop by itself doesn’t damage Facebook, at least in immediate financial terms. It still raised $16 billion selling stock.

“The people who have to worry are the people who bought the stock on Friday,” Summer said.

Indeed, the drop is likely to anger investors, and it led Monday to a round of speculation about why Facebook isn’t worth as much as some people thought.

The long-standing question about Facebook is how it will make money from its users, who now number roughly 900 million around the world.

For the most part, the answer has been advertising, and the company has at times struggled in those efforts, particularly in persuading advertisers that having their brand appear on Facebook will stimulate sales.

In the days leading up to the stock offering, one of the nation’s biggest advertisers, General Motors, landed a roundhouse in the business world.

The carmaker said it would no longer buy advertising from the site. Not much money was involved — General Motors was reportedly spending $10 million annually — but it underscored complaints that major advertisers were frustrated with the company.

In addition, Facebook’s profit dropped 12 percent in the first quarter from the corresponding period last year to $205 million, as costs grew faster than revenue.

Despite the setbacks, Facebook was very aggressive about assessing its worth.

One way that analysts measure such things is by comparing a share’s price to its earnings, or P/E ratio, and on this, the Facebook price of $38 appears relatively high. On a projected earnings basis, Facebook put its price at more than 50 times its earnings. By comparison, Google, Apple, Zynga and Groupon all had ratios less than 20, according to data from FactSet Research.

Even so, many analysts spoke highly of the company, which has evolved from an idea hatched in a university dorm into a company that, even with yesterday’s losses, is valued by the market at $93 billion, roughly the same magnitude as an established American icon such as McDonald’s.

Facebook is “in an experimentation mode — maybe monetizing social users isn’t as easy as they hoped,” said Brian Blau, research director of consumer technologies at Gartner. “In the long term, I think this will look like just a bump in the road.”

(Washington Post Co. Chairman Donald E. Graham is a member of Facebook’s board.)