SUNNYVALE (AP) — Yahoo (YHOO) is still struggling to boost revenue nearly three years into CEO Marissa Mayer’s tenure, magnifying concerns that the Internet company holds little value beyond its lucrative Asian investments.

The latest evidence of Yahoo’s financial malaise emerged Tuesday with the release the company’s first-quarter earnings report.

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After accounting for ad commissions, Yahoo’s revenue fell 4 percent from the same time last year to $1.04 billion, extending a troubling trend that began before Mayer took over. That downturn overshadowed an 8 percent increase in Yahoo’s total revenue, before commissions, because investors focus on the amount of money that the company retains after paying its partners for helping to draw online traffic to it ads.

Those expenses, known as “traffic acquisition costs,” quadrupled from the same time last year, an indication that Yahoo is paying a steep price to show its advertising.

The Sunnyvale company also poured substantially more money into developing new products, contributing to a steep drop in Yahoo’s first-quarter earnings. Investors already had driven down the company’s stock by 12 percent so far this year before Tuesday’s numbers came out. The shares shed another 67 cents to $43.82 in extended trading.

Mayer has been trying to revive Yahoo since becoming CEO in July 2012, but her efforts have been mostly unsuccessful despite a boom in the digital advertising that generates most of the company’s revenue. Most of the marketing money is still flowing to Google and Facebook — a pair of companies that have supplemented their powerful advertising networks with a variety of services and features that keep people coming back.

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Things were supposed to change under Mayer, a respected executive who helped build Google into the Internet’s most powerful company during her tenure there. But investors appear to be losing faith now that Yahoo’s revenue, after ad commissions, has declined from the previous year in eight of the past nine quarters. The only uptick, in last year’s third quarter, reflected a mere 1 percent increase in revenue.

Signaling her own dissatisfaction with the company’s progress, Mayer recently reshuffled Yahoo’s top management. She also re-negotiated the terms of Yahoo’s 5-year-old search partnership with Microsoft Corp. to give Yahoo a bigger cut of the companies’ shared revenue, more control over the results on Yahoo’s site and the option to sell more ads through other networks besides Microsoft’s.

“Yahoo is amidst a multi-year transformation to return an iconic company to greatness,” Mayer said Tuesday in a statement.

Although Yahoo’s stock has nearly tripled under Mayer’s leadership, the run-up hasn’t been driven by the company’s core business. Most of the increase has been tied to Yahoo’s 24 percent stake in Alibaba Group, an e-commerce star in China. Yahoo’s Alibaba holdings are currently worth $32 billion, accounting for about three-fourths of Yahoo’s current market value.

Pressured by shareholders, Mayer in January announced plans to spin off the Alibaba stake into a separate company by the end of this year. The spinoff is designed to avoid paying a large tax bill on the gains from that investment.

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Yahoo also owns a 35 percent stake in Yahoo Japan. The stake is currently worth nearly $9 billion, before the taxes on the gains that the company eventually will realize. Throw in the nearly $7 billion in cash and marketable securities that Yahoo held at the end of March, and the company’s current market value of $42 billion implies investors think Yahoo’s ongoing business is worth next to nothing.