Generation Z (16- to 24-year-olds) is considered America's first "digitally native" generation. These younger Americans frequently use mobile apps and social networks, but they mostly avoid Facebook (NASDAQ:FB), which is more popular with millennials.

Last year, a Piper Jaffray survey found that only 9% of teens considered Facebook their preferred social media platform. The vast majority preferred Snap's (NYSE:SNAP) Snapchat, as well as Instagram, which is owned by Facebook.

A large number of Gen Zers are also devoted to Alphabet's (NASDAQ:GOOG) (NASDAQ:GOOGL) YouTube, which is technically a social network. Last year, an AdWeek survey by Defy Media found that 50% of Gen Zers couldn't "live without" YouTube. A more recent survey by VidMob revealed that more than half of Gen Zers had increased their usage of YouTube, Snapchat, and Instagram over the past year.

Chart showing Gen Z usage of YouTube, Snapchat, and Instagram.

Data source: VidMob. Chart by author.

These numbers indicate that Facebook and Google should retain their duopoly on digital ads in America. That's why eMarketer expects those two companies to control 57.7% of the U.S. digital advertising market this year. However, the figures also suggest that Snap -- which has been struggling with slowing user growth -- isn't down for the count just yet.

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Leo Sun owns shares of Facebook. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), and Facebook. The Motley Fool has a disclosure policy.