Disappointing results from Walt Disney Co. after the close of trading Tuesday sparked the rout. Selling spread to other television and publishing companies as quarterly reports from CBS Corp. to 21st Century Fox Inc. and Viacom Inc. were marked by shrinking U.S. ad sales and profits propped up by stock buybacks. Viacom fell 14 percent Thursday, its biggest drop since October 2008, while Fox slid 6.4 percent.

ValueAct Holdings LP, an activist investment firm run by Jeffrey Ubben, disclosed a 5.5 percent stake in Fox’s Class B shares on June 6, while Elliott Management Corp., a hedge fund run by Paul Singer, is the seventh-biggest holder of the stock, with a 1.9 percent stake as of March 31.

A spokesman for Elliott declined to comment, and Briana Zelaya of ValueAct didn’t immediately respond to a phone call seeking comment.

Tensile Capital LLC, a San Francisco-based fund, owns 1.2 percent of News Corp.’s Class B shares as of the end of the first quarter, making it the eighth biggest holder. It was the third-largest U.S. public equity position for the firm at the end of the first quarter, accounting for 9.8 percent of that portfolio.

Arthur Young, portfolio manager at Tensile, declined to comment.

Evaporating Value

The fourth-biggest stake in Viacom’s Class A shares is with Ionic Capital Management LLC, according to a March 31 regulatory filing. Ionic’s largest U.S. stock position is another media company, Media General Inc., which makes up 5 percent of the firm’s disclosed stock holdings. Media General slumped 11 percent on Thursday.

Caroline Quinn, associate director of investor relations at Ionic, didn’t immediately return a phone call seeking comment on the stock moves.

Until Tuesday, media shares were the best-performing stocks of the bull market, rising 531 percent to eclipse automakers, retail stores and banks. The industry’s market capitalization was about $650 billion, compared with $135 billion in March 2009.

That value is evaporating. In just five stocks -- Disney, Time Warner Inc., Fox, CBS and Comcast Corp. -- almost $50 billion of value has been erased in two days.