Ironfire Capital's Eric Jackson told CNBC he believed Mayer's turn around of the company had thus far proven disappointing, especially since activist investor Starboard Value began agitating for changes.
"It's been six months [since Starboard began speaking up] and these results are very underwhelming," Jackson said. "I think investors are wanting to know when do we actually start to see a 'Marissa premium' built into these shares rather than a 'Marissa discount.'"
Display advertising revenue (excluding traffic acquisition costs), an area of focus for the company, fell 7 percent from the year ago to $381 million. Total GAAP display revenue saw a 2 percent gain—which would mark the first Q1 growth in this metric since 2011, Mayer said on the firm's earnings webcast.
Read MoreFmr. Yahoo CEO: Marissa Mayer may have to go
Yahoo said its price-per-ad fell about 17 percent compared to the same period in 2014.
Mayer revealed on the webcast that Yahoo is working to develop a plan for its stake in Yahoo Japan (a joint venture with SoftBank), and that the company had been advised not to include that stake in its proposed Alibaba spin-off. She said the options "require careful study," and that the company would share the details of any eventual plan on future earnings calls.
Following the earnings release, Yahoo said it expected to see its second-quarter revenue (excluding traffic acquisition costs) between $1.01 billion and $1.05 billion. The guidance midpoint was slightly below the consensus estimate of $1.04 billion.
There were some bright spots for the tech giant, however, as search revenue increased 20 percent from a year ago, to $956 million. Search volume rose to a five-year high on the strength of a partnership with Mozilla, Yahoo said. Mayer called this a "high-quality" deal.
"We are even more excited about that partnership today than we were when we signed it," she said of the Mozilla deal. Still, she added, future deals would need to be similarly profitable.
Mobile user growth and GAAP revenue also saw sizable gains, the CEO said, adding that the company's more than 20 percent year-over-year growth for mobile monthly active users underscored its commitment to being "mobile-first."