Yahoo said Tuesday it will make deep cuts to its business, including laying off 15 percent of its global workforce, nearly 1,600 people, and closing five offices. The company also said for the first time it would consider selling its Internet properties.

“Today we’re announcing a strategic plan that we strongly believe will enable us to accelerate Yahoo’s transformation,” Yahoo CEO Marissa Mayer said in a statement.

Mayer will address investors and review the company’s fourth quarter earnings results in a presentation that begins at 2 p.m. Observers said the call is a key moment for Mayer, who must convince upset shareholders that her vision to turnaround the company over several years by investing in people and products is the right call.

“(This) is her most important earnings call since she became CEO and could set the tone for a very difficult year or she finds some magic and backs off the activist and investment community which is feeling worried right now,” said a former Yahoo executive who declined to be named.

In a press release, Mayer said she would narrow Yahoo’s focus to three main products: Search, Mail and Tumblr and four verticals — News, Sports, Finance and Lifestyle. Those would exist in the U.S., Canada, United Kingdom, Germany, Hong Kong and Taiwan.

Yahoo said it plans to close five offices in Dubai, Mexico City, Buenos Aires, Madrid and Milan.

It’s unclear whether this refined focus will be enough to satisfy upset shareholders who are considering launching a proxy battle against Yahoo, where they would suggest their own slate of candidates.

Board chairman Maynard Webb said in a statement that Yahoo will explore “additional strategic alternatives,” adding, “we will engage on qualified strategic proposals.”

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Eric Jackson, a managing director at SpringOwl, told The Chronicle last week he’ll be watching whether Yahoo will choose the following options: replacing Mayer, putting the company up for sale or entering into a strategic partnership. If none of those three things happens, he doesn’t think shareholders will be satisfied.

“Just doing some (job) cuts, whether it’s 10 percent or 25 percent or 35 percent, still doesn’t solve the problem that you still have Marissa Mayer running the company with the existing board,” Jackson said.

Mayer also said she plans to grow Yahoo’s business in mobile, video, social and native advertising.

Selling the core business to potential strategic buyers like Verizon or private equity firms could result in even more layoffs once the deal is closed, analysts said. And when Yahoo employees go looking for new jobs, the Yahoo brand doesn’t carry the weight it used to, said Nick Parham, a San Francisco career counselor, who has clients that work at Yahoo.

Parham said if he was a hiring manager with resumes from job candidates coming from Google, Facebook and Yahoo, he would look at the Yahoo employees last.

“There is no doubt that coming from a brand that is receeding in prominence is not a good thing,” Parham said. In general, people that come from succcessful companies are “probably highly motivated and probably a strong talent,” he added.

“I wouldn’t want to go out and hire talent from a company that is stagnant and not going anywhere. It begs the question why would someone be with a company like that?” Parham said.

Wendy Lee is a San Francisco Chronicle staff writer. E-mail: wlee@sfchronicle.com Twitter: @thewendylee