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Kathy Savitt is leaving Yahoo to join STX Entertainment.Credit Cindy Ord/Getty Images for Yahoo

SAN FRANCISCO — The executive who expanded Yahoo’s ambitious efforts to make itself a digital media force is leaving the company after some of its recent projects have struggled to gain attention from viewers and advertisers.

Kathy Savitt, who oversaw Yahoo’s digital media projects, said on Friday that she was leaving the Internet company to join STX Entertainment as its president for digital operations.

Under Ms. Savitt’s media projects leadership, Yahoo started more than a dozen digital magazines in the United States, struck a partnership with Live Nation to webcast a live concert every day, revived the “Community” television series as a Yahoo show and commissioned two original streaming series.

Yet some of the company’s media projects have struggled to gain traction with viewers and advertisers in the face of intense competition from big rivals like Amazon, Netflix, Facebook and Google, as well as topic-specific sites focusing on food, technology and other areas.

Yahoo, under its chief executive, Marissa Mayer, is also facing more fundamental questions about its future.

This week, Yahoo said it was rethinking its planned spinoff of its 15 percent stake in Alibaba, a Chinese e-commerce company, after it did not receive indications from United States tax authorities that the transaction would be tax-free. And Ms. Mayer’s three-year effort to turn around the company’s core advertising business has failed to impress investors.

Yahoo has also had a great deal of change at the executive level over the last year. Ms. Mayer appointed a new head of North American advertising, Lisa Utzschneider, last October, eventually leading to the departure of two other top ad executives. In April, she shuffled much of her top leadership team.

Yahoo said in a statement that it appreciated Ms. Savitt’s contributions; the company added that advertisers such as Honda and Kia have responded positively to digital media efforts like video.

STX, founded last year, is so far best known for its wild ambition. It has released only one movie — a small-budget horror film called “The Gift,” which has taken in $40.8 million — but plans to produce and distribute as many as 15 a year, more than studios like Paramount Pictures. Backers and partners include TPG Capital and Huayi Brothers Media, a Chinese entertainment company. STX has said it would spend roughly $1 billion annually to make, market and distribute movies.

Speaking by phone from Singapore, Robert Simonds, STX’s chief executive, said Ms. Savitt would spend “a few hundred million” dollars a year to produce content aimed at digital platforms. He declined to say which ones, but the opportunity appears to be in supplying to both established players like Netflix and social media companies like Facebook and Snapchat.

“Our goal is very simply to mimic in digital what we are doing on the movie side,” he said. “There is a huge opportunity, and we’re going to spend a lot of money.”

Mr. Simonds declined to say how long talks had been underway with Ms. Savitt. “We met with pretty much every executive out there,” said Sophie Watts, president of STX, also speaking from Singapore. Ms. Watts said that a friend told her Ms. Savitt was “ungettable, but if you can convince her to come she is the perfect person.”

Yahoo did not name an immediate successor to Ms. Savitt. But the company said it had a deep bench of talent working on its media projects, including Martha Nelson, the former editor in chief of Time Inc. who joined Yahoo in a similar role last month, and Debra Berman, former chief marketing officer of J. C. Penney, who became Yahoo’s senior vice president for consumer marketing in June.

A spokesman for STX said Ms. Savitt was not available for an interview. In a statement, Ms. Savitt said STX was “creating a new way for audiences to access meaningful stories, from wherever they are.”

STX faces enormous hurdles. It is extremely difficult to weather the inevitable movie hits and misses without the steady revenue that comes from a library of past films. Even Steven Spielberg, David Geffen and Jeffrey Katzenberg — the trio initially behind DreamWorks — struggled to pull it off.

STX has moved quickly to secure favorable release commitments with theater chains and multiyear deals with cable networks like Showtime to run its movies. STX has a deal with Universal to handle home video. Movies in the STX pipeline star the likes of Matthew McConaughey and Julia Roberts.

The management of STX notably has something to prove to Hollywood, which seems to be driving its early success: Several senior executives joined the upstart studio after being pushed out of top jobs at movie companies like 20th Century Fox and Universal.