SAN FRANCISCO (MarketWatch) — Facebook Inc.’s IPO was not the soaring rocket ship everyone had been expecting.

There were a few factors at play: the general overall jittery stock market, with the Dow falling 12 out of the last 13 trading days, combined with the huge float of shares offered in the market — a whopping $16 billion worth — that ultimately gave Facebook a valuation of nearly $105 billion.

Facebook hosted a “Hackathon” at its Menlo Park headquarters on May 17, the day before its initial public offering. Facebook

“It feels pretty muted,” said Sam Hamadeh, the chief executive of PrivCo, as he was leaving the morning circus atmosphere at the NASDAQ in New York’s Times Square. The biggest tech IPO ever, Facebook FB, +1.93% was priced at the top of the expected range at $38, it opened above $42, fell back to $38, rose and then fell again. At the end of the day, Facebook shares closed 23 cents above their IPO price.

Institutional and retail investors were grumbling throughout the day. They had invested with the hopes of a much bigger one-day pop. As the stock hovered in flat territory near the closing bell, Timothy Collins, principal and chief investment officer of TangleTrade Advisors in Austin, Texas, was the voice of many investors when he tweeted, “$FB at $38 is starting to feel like the Alamo.” Read more about Facebook's sputtering IPO.

But the bottom line of the day was that the deal was mostly a good one for the company. Now the pressure is on to maintain that lofty valuation.

“The underwriters did a great job of pricing the IPO,” said Rocky Agrawal, principal analyst at reDesign mobile, a consulting firm. “They didn’t look like they left too much money on the table...They [the underwriters] stepped in and stabilized the stock when it hit $38. That is all the things they should be doing....It’s a good day, the markets have shown that they are fairly efficient.”

The social media giant raised a hefty $16 billion, much of which will go into the company coffers. It also created a host of newly minted billionaires and millionaires, from its 28-year-old founder/CEO Mark Zuckerberg, down to most of Facebook’s 3,500 employees.

The IPO also further padded the big pockets of a who’s who list of Silicon Valley investors, including Netscape founder and Facebook board member Marc Andreessen and billionaire libertarian Peter Thiel. The list of investors also included U2 front man Bono and Microsoft Corp. MSFT, -1.04% .

Now, the challenge for investors will get tougher. The underwriters providing support of the stock at $38 reminded me a little bit of J.P. Morgan and his firm’s effort to staunch the selling during the 1929 stock market crash. Investors may now worried about where Facebook is going to trade next week.

Hamadeh noted that the last time underwriters stepped in to provide support for an IPO was during Zynga’s first day of trading in December, when it priced at $10 but immediately began trading below that price.

The fact that Facebook’s shares had to be supported by the underwriters “augurs poorly for Facebook’s stock,” he said in an e-mail after the close. He said that move indicated that the pent-up demand for Facebook shares was mostly wiped out when its underwriters increased the IPO size by 25% in the last two days of the deal. He said he believes the stock is fairly valued at $24-$25.

The big question now is how long can Facebook support its $104 billion valuation? At its current price of $38, it is trading more than 78 times estimated earnings for this year, according to a consensus estimate of 49 cents from Thomson Reuters on Friday.

Analysts have forecast that it is going to be some time before the company is able to generate bigger revenue growth from advertising. But its revenue growth decelerated in the last quarter, so an investment now at this valuation is a big bet on hope.

Facebook IPO: Fanfare or fumble?

“It’s going to take a long time for the company to grow into its $105 billion valuation,” said Agrawal.

Don’t expect Zuckerberg to be focused on the company’s stock price. Facebook hosted an all-night hackathon at its Menlo Park, Calif. headquarters on the eve of the IPO, as a way to show it was still focused on its business. Zuckerberg also wore his signature hoodie to speak to Wall Street during the road show, a message that seemed to say he was only doing the IPO because he had to.

Indeed, in his comments while ringing the NASDAQ opening bell from Menlo Park, he said going public was an “important milestone” in Facebook’s history. “But here’s the thing. Our mission isn’t to be a public company,” Zuckerberg said. “Our mission is to make the world more open and connected.”

Zuckerberg’s comments echo those of the Google Inc. GOOG, +0.32% co-founders at the time of their IPO, who told Wall Street they would not be focused on quarterly earnings. The result has been a stock that has seen strong gains over the last 8 years - along with a lot of dips.

Investors perhaps should buckle their seat belts.