The deepening slide in Facebook Inc.'s stock is fueling talk once considered implausible on Wall Street and in Silicon Valley.

Should Mark Zuckerberg, the social media visionary but neophyte corporate manager, step aside as CEO to let a more seasoned executive run the multibillion-dollar company?

In that scenario, Zuckerberg would remain as the creative force propelling Facebook’s technological innovation. But the 28-year-old would cede the CEO title to someone better suited to overseeing operations and building rapport with finicky investors — mundane but essential duties for which Zuckerberg has shown little appetite or aptitude.

“There is a growing sense that Mark Zuckerberg, talented though he may be, is in over his hoodie as CEO of a multibillion-dollar public company,” said Sam Hamadeh, head of research firm PrivCo. “While in many cases a company founder can, and does, grow into the job, things are happening so quickly that there is precious little time here for Zuckerberg to do that.”

Doubts about the Facebook founder intensified Thursday as the stock closed below $20 for the first time. The shares, which slipped to $19.87, have shed nearly half their value since Facebook’s disastrous initial public offering three months ago.

Thursday’s selling was driven by the expiration of provisions that had barred Facebook’s venture capital backers from unloading their shares. Trading volume was abnormally heavy, a sign of the fury with which some of the company’s earliest investors ran for the exits as soon as they could.

“This was the most anticipated IPO in many years and it was like an exploding cigar,” said Barry Ritholtz, head of research firm Fusion IQ. “Every investor thought they were about to become wealthy beyond their wildest dreams, and they had this blow up in their face.”

The danger, Ritholtz said, is that the drooping stock price could tag the company itself with a “stink of failure” that could make advertisers less willing to use Facebook.

Facebook’s troubles stem from numerous factors, including investors’ overinflated expectations, the company’s unproven strategy for mobile advertising and an IPO that was mangled by both the Nasdaq stock market and Facebook’s investment banks. Its first-ever earnings as a public company, released last month, beat analysts’ expectations as revenue grew 32% year over year. Still, the stock plunged as investors were spooked by rising costs and slowing growth.

Only some of those problems are attributable to Zuckerberg, analysts say. And given that he is the company’s largest shareholder, with ironclad control over all decisions, nothing would happen without Zuckerberg’s assent.

Still, restless investors blame Zuckerberg for several missteps, such as pricing the IPO at a stratospheric $100-billion valuation.

Facebook boosted its IPO price days before the offering, with several large shareholders selling unexpectedly large chunks of their holdings. The moves were seen as siphoning extra profit for the company and big shareholders at the expense of subsequent investors.

The enormous valuation left Facebook little room for error, and was seen as hubris by a company that at the time saw few obstacles in its path.

Zuckerberg’s indifference to traditional corporate etiquette — he wore sneakers and his trademark hoodie for Facebook’s first big investor meeting — is viewed as disrespectful of the corporate world he needs to win over.

“His behavior is what I would expect of someone his age — the hoodies and everything else,” said Chris Whalen, senior managing director at Tangent Capital Partners in New York. “He’s trying to appeal to his audience instead of being responsible to his investors. His job now is to run the company.”

Even Apple Inc.co-founder Steve Jobs, who was known for favoring turtlenecks and jeans, donned a suit in his early days when he was touting his upstart.

Some experts say the criticism of Zuckerberg is overdone.

The stock has fallen because investors have realized that Facebook’s growth potential isn’t as great as they had thought, analysts said.

“Is it possible that management changes could improve those prospects? Maybe, but I don’t think it’s a sure bet,” said Dan Alpert at New York investment bank Westwood Capital. “Zuckerberg appears to be a decent guy who the market should give a little bit longer to prove his mettle.”

There is precedent for iconic founders to hand off CEO duties.

Larry Page led Google Inc.in its early days, but he and co-founder Sergey Brin, both in their late 20s, were persuaded to bring in technology industry veteran Eric Schmidt to provide “adult supervision” in 2001 when the search company was still privately held.

“Mark Zuckerberg should be the chief product officer and bring in a whole slew of new management that have a very long track record in running companies, like Google did,” said Scott Sweet, senior managing partner of Tampa-based IPO Boutique.

Zuckerberg and his lieutenants have tried in vain to reverse investor skepticism.

But they’ve been stymied by the difficulty in determining Facebook’s actual value because the business models of social media companies are unproven.

Although Facebook has nearly a billion users, no one is sure whether advertisers can gain traction in selling products to them.

The challenge for Facebook’s stock could worsen in coming months.

Facebook freed up about 271 million shares Thursday, adding to the 421 million the company sold in the IPO. An additional 192 million will be released in mid-October and a whopping 1.2 billion shares in mid-November.

Many investors are hesitant to buy Facebook shares until that cloud is lifted.

“Whatever happens this week is a dress rehearsal for November,” said Kevin Landis, chief investment officer at Firsthand Capital Management in San Jose.

Investors hope Zuckerberg will be able to win over skeptics by then.

“Mark Zuckerberg has not yet proven himself a success or a failure,” said Michael Pachter, an analyst at Wedbush Securities.

walter.hamilton@latimes.com

jessica.guynn@latimes.com