Yahoo posted first-quarter revenue that beat analysts' estimates slightly, but the 11.3 percent decline shows the web pioneer's struggle to boost growth its core online search and display advertising business. Yahoo's total revenue fell 11.3 percent to $1.09 billion in the first quarter ended March 31. This was the first decline after four straight quarters of growth.

After deducting fees paid to partner websites, Yahoo's revenue fell to $859.4 million from $1.04 billion.

"I’m pleased that we delivered Q1 results in line with our expectations. Our 2016 plan is off to a solid start as we continue to focus on driving efficiency, lowering costs, and improving long-term growth," said Marissa Mayer, CEO of Yahoo. "In tandem, we made substantial progress towards potential strategic alternatives for Yahoo. Our board, our management team, and I are completely aligned on this top priority for shareholders."

While Yahoo runs some of the world's most-read websites, it has been unable to keep up with Google and Facebook in the battle for online advertisers.

Under pressure from activist investors, Yahoo launched the auction of its core business in February after shelving plans to spin off its stake in Chinese e-commerce giant Alibaba Group Holding Ltd. It has also said it could spin off the business.

The first round of bids for interested parties closed on Monday, according to media reports. Verizon Communications Inc is reportedly the favorite to win the auction, with Britain's Daily Mail newspaper the latest firm to express interest.