SAN FRANCISCO — Marissa Mayer, just by being Marissa Mayer, has done more to move Yahoo forward in her first six months as chief executive than any of her five predecessors did over as many years.
An accomplished engineer and executive, Ms. Mayer joined Yahoo from Google as a Silicon Valley celebrity. Since then, just her presence at the company's Sunnyvale, Calif., headquarters seems to have jolted Yahoo back to life. On Monday, Yahoo reported a good quarter, increasing revenue for the first time in four years and beating Wall Street expectations by 30 percent.
That pushed Yahoo's stock to $20.91 in after-hours trading — a four-year high (but still well below the $31 Microsoft offered the company back in 2008).
(Read More: Yahoo Earnings: Is Marissa Mayer's Plan Working?)
Ms. Mayer attributed growth to a renewed focus on "people and products" in a call with analysts on Monday.
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She has added new Yahoo fans by revamping Yahoo's e-mail service and redesigning Flickr, the firm's photo-sharing app, which sent the number of photo uploads rising 25 percent. Ms. Mayer said those improvements were a hint of more under way.
"We are off to a very good start," Ms. Mayer told analysts. "We are making the world's habits more inspiring and entertaining."
She has also introduced several morale boosters since joining the company — including free cafeteria food and new iPhones and Android-powered phones — to staff members who were more accustomed to cost-cutting and layoffs. In a further sign that the company was no longer considered a sinking ship, she lured another Silicon Valley tech star, Max Levchin, a PayPal co-founder, to Yahoo's board last month.
But those were just the office things. Analysts were more impressed with improvements to the company's search business. Yahoo outsourced it to Microsoft in 2009 and it has languished ever since, propped up only because of a revenue-guarantee clause in its contract with Microsoft that is set to expire in March. Yahoo's search revenue rose 4 percent in the fourth quarter, to $482 million, compared with $465 million for the period a year earlier.
Over all, Yahoo reported net income in the fourth quarter of $272.3 million, or 23 cents a share, compared with $295.6 million, or 24 cents a share, in the period a year earlier.
Revenue was up 1.6 percent, to $1.35 billion.
(Read More: Yahoo Earnings Beat; Revenue Outlook Is Light)
The improvement to its search business, however, was offset by continued declines in Yahoo's display ad revenue. The company said it made $591 million in display ad sales last quarter, a 3 percent decline from the $612 million in the quarter a year ago.
Yahoo, once the biggest seller of display ads in the United States, went from a leading 15.5 percent share of all digital ad revenues in the United States in 2009, to an 8.4 percent share last year, even as total digital ad spending grew, according to eMarketer. Meanwhile, its competitor, Google, increased its share to 41 percent.
"More personalized content and increased product innovation will be key to getting us back to the path for display revenue growth," Ms. Mayer said on the call.
The fourth-quarter results impressed analysts, but many remained skeptical.
"Marissa will have to protect Yahoo's legacy business while positioning the company for future growth," Colin Gillis, an Internet analyst at BGC Partners, said in an interview Monday. "That is not easy."
With Ms. Mayer's honeymoon with Wall Street expected to end soon, investors are eager to see whether she can deliver sustained growth. Yahoo, with 700 million monthly users, commands one of the largest audiences on the Web. But until now the company, an Internet pioneer, has been unable to translate its users into sustainable profits.
As Ms. Mayer has acknowledged, Yahoo's future growth may well depend on its mobile strategy. And without mobile hardware like a tablet computer, a browser or a mobile operating platform of its own, Yahoo has a long way to go.
The company continues to be outspent in research and development by Google, Apple, Facebook and Amazon. It also continues to have a hard time convincing Silicon Valley's engineering talent to join Yahoo instead of its competitors.
Ms. Mayer has said Yahoo's mobile growth may come from acquisitions of mobile app companies. In six months, Ms. Mayer has acquired three start-ups — Stamped, OnTheAir and Snip.it — for undisclosed sums, more for the engineering talent than the products.
But, chances are it will be a long, slow slog. "The road will only get harder," said Mr. Gillis. But compared to Ms. Mayer's disgraced immediate predecessor, Scott Thompson, who left the company after four months over embellishments on his resume, Mr. Gillis added, "at least she got a honeymoon."
—Disclosure: CNBC has a content-sharing partnership with Yahoo's finance site.