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The NFL player Marshawn Lynch played tug-of-war at a Nickelodeon awards show last month.Credit Kevin Winter/Getty Images

It is no more than a coincidence that Viacom announced weak earnings and suffered a sharp plunge in its stock on the same day that one of its biggest stars, Jon Stewart, exited the stage.

Still, Mr. Stewart’s departure from “The Daily Show” on Comedy Central on Thursday could be a metaphor for the broader woes facing Viacom’s constellation of cable television networks, which also includes MTV, Nickelodeon, VH1 and Spike.

Once known for its cachet with younger viewers, Viacom now is struggling to shift its business as a generation of iPhone-wielding, social-network-using, online-streaming viewers abandons traditional television.

Ratings across Viacom’s bundle of networks tumbled an estimated 18 percent during the quarter that ended in June, according to one analyst’s estimates. Programs it deemed hits — “Scream” on MTV and “Lip Sync Battle” on Spike — failed to reverse the persistent ratings declines plaguing the company.

Even at Comedy Central, home to the critically acclaimed “Broad City” and of-the-moment comedians like Amy Schumer, Michael Key and Jordan Peele, ratings fell an estimated 12 percent during the quarter.

Advertisers still trade on those figures, and those eroding ratings led to a 9 percent drop in domestic advertising revenues during the latest quarter, Viacom reported on Thursday, a figure much higher than analysts had expected. Viacom’s efforts to introduce new audience metrics that capture viewing on digital outlets, as well as data-driven, digital advertising technologies, have mitigated those declines but have yet to return the advertising business to growth.

Viacom’s results, which caused shares to fall more than 14 percent, to $44.10, only deepened the anxiety about the health of the media business on a day when questions about the future of traditional TV dominated Wall Street.

Eight major media stocks suffered an abrupt and startling crash on Wednesday, eliminating a combined $37 billion in market value. Fears about cord cutting combined with worries about sharp ratings declines and weak advertising sales prompted the mass sell-off. The collapse largely continued on Thursday, led by Viacom’s steep decline.

“Investors are moving en masse out of media,” said David Bank, an analyst with RBC Capital Markets, who said he was “calling from the vortex of media hell.”

Of all the media companies, Viacom was particularly hard hit, with its core demographic of children and teenagers — the group moving fastest away from traditional television. Marketing executives said that Viacom, which used to dominate the youth advertising market, now faces intense competition for their ad dollars from Facebook, YouTube and other digital outlets.

“The younger and more valuable demographics are seeking their entertainment elsewhere, and watching less TV than ever before” said Ian Schafer, chairman of Deep Focus, a New York-based ad agency. “Other brands are taking the mantle from Viacom — everything from Vice to the universe of YouTube stars.”

In another blow to the company, Viacom reported a slowdown in its domestic affiliate fees — the money it receives from cable and satellite distributors — to mid-single-digit growth during the quarter that ended on June 30.

Some smaller cable companies have dropped Viacom networks from their lineup, leading to fears that larger cable and satellite companies will eventually follow their lead.

“We believe Viacom’s brands are the worst positioned in the future environment,” Todd Juenger, a media analyst with Bernstein, said in a research note.

Another uncertainty facing the company are questions over who will succeed Sumner Redstone, 91, Viacom’s chairman and controlling shareholder. Mr. Redstone, who controls about 80 percent of the company, said in a statement in May that decisions over succession would be made by the board, not an individual, and that such decisions had not yet been made.

In its earnings report, Viacom said that its profits fell to $591 million during the quarter, down from $610 million during the same period last year. That was primarily because its film division, Paramount, had no theatrical releases in the quarter, compared with last year, when it released “Transformers: Age of Extinction.”

Total revenues missed expectations, falling 11 percent to $3.1 billion during the quarter, dragged down by a 44 percent decline in its filmed group. Sales in its media networks group were flat, with higher affiliate fee revenues offsetting ad declines.

Suddenly, Plenty of Options for Cord Cutters Here are some prominent services offering live TV, à la carte networks and other on-demand streaming options.