Twitter is now so ubiquitous in American culture that even the venerable New York Times has added phrases like “Twitter storm” to its vocabulary. The Times was using Twitter storm as far back as November 2010 to describe a media controversy surrounding — who else? — Kanye West.

But in 2015, Twitter is seeing its supremacy challenged by a new rival, Instagram. And while “Instagram Storm” isn’t quite as catchy, the media is desperately trying to coin some phrase to describe a major milestone. This week, ABC News reported on the “Insta-Surge,” when the photo-sharing app gained more active users than Twitter. In the past nine months, more than 100 million new users have joined Instagram, for a total of 400 million people filtering, hashtagging and sharing their pics. For comparison, Twitter has a measly 316 million active user base.

Twitter first rose to popularity on the backs of celebrities, who used the social media platform to connect with fans and show off their rich-and-famous lifestyles. Social media apps let popular A-listers like Rihanna, Miley Cyrus, and the Kardashian Klan invite followers to see their daily lives up close and personal; Twitter and Instagram are the new venues for brands looking to hire a celebrity spokesperson.

“We’re seeing a landslide usage transfer of younger demographics over to Instagram,” says Christopher Lawrence, CEO,Celebrity Endorsement Agency, Inc. “While Boomer and Gen X celebrities still primarily use Facebook and Twitter to share and communicate, the quick and streamlined properties of Instagram satisfies both the highly visual and “always on” needs of millennial stars and their fans.”

Every day, more than 80 million photos are posted with Instagram. Big-name celebs like David Beckham and Caitlyn Jenner recently signed up, while at the same time, Instagram is trying to monetize the app with sponsored posts.

“There is a battle royale for mobile ad dollars, and that is what the investors are trying to figure out. Who is best positioned?” said Daniel Ives of research group FBR Capital Markets. “Twitter has definitely hit some speed bumps over the past year.”

Not only has social media created new opportunities for celebrity endorsement advertising, it’s also created a new class of celebrities altogether. These so-called social media “influencers” are also making millions from celebrity product endorsements, even though most people would never recognize their names. These hip young Millennial influencers have built up massive social media followings, particularly among teens.

And in 2015, whether on Instagram or Twitter, that gives them real power.