On May 20, 2013, Mayer led Yahoo! to acquire Tumblr in a $1.1 billion acquisition. In February 2016, Yahoo! acknowledged that the value of Tumblr had fallen by $230 million since it was acquired. In July 2013, Yahoo! reported a fall in revenues, but a rise in profits compared with the same period in the previous year. Reaction on Wall Street was muted, with shares falling 1.7%. In September 2013, it was reported that the stock price of Yahoo! had doubled over the 14 months since Mayer's appointment. However, much of this growth may be attributed to Yahoo!'s stake in the Chinese e-commerce company Alibaba Group, which was acquired before Mayer's tenure.
In November 2013, Mayer instituted a performance review system based on a bell curve ranking of employees, suggesting that managers rank their employees on a bell curve, with those at the low end being fired. Employees complained that some managers were viewing the process as mandatory. In February 2016, a former Yahoo! employee filed a lawsuit against the company claiming that Yahoo's firing practices have violated both California and federal labor laws.
In September 2013, Mayer became the first CEO of a Fortune 500 company to be featured in a Vogue magazine spread.
In 2013, she was also named in the Time 100, becoming the first woman listed as number one on Fortune magazine's annual list of the top 40 business stars under 40 years old. Mayer made Fortune magazine history in 2013, as the only person to feature in all three of its annual lists during the same year: Businessperson of the Year (No. 10), Most Powerful Women (at No. 8), and 40 Under 40 (No. 1) at the same time. In March 2016, Fortune then named Mayer as one of the world's most disappointing leaders.