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 (META -1.38%), 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 (SNAP 0.78%) Snapchat, as well as Instagram, which is owned by Facebook.

A large number of Gen Zers are also devoted to Alphabet's (GOOG 1.44%) (GOOGL 1.89%) 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.