As more adults join Facebook (NASDAQ:FB), more teens are retreating to Snap's (NYSE:SNAP) ephemeral messaging app Snapchat to avoid their parents' prying eyes.

Piper Jaffray's biannual "Taking Stock with Teens" survey confirmed that trend, with 47% of surveyed teens calling Snapchat their "favorite" social networking media platform -- up from 35% a year earlier.

A chart comparing the popularity of social networks among US teens.

Data source: Piper Jaffray. Chart by author.

That seems like bad news for Facebook, but Instagram -- which is owned by Facebook -- is holding steady with teen users. Instagram has also been adding Snapchat-like features -- disappearing messages, face masks, and video "stories" -- to lure away Snapchat's users.

That strategy is paying off. Instagram hit 500 million daily active users in September, up from just 200 million in April. Snapchat's daily active users rose just 3% sequentially to 178 million last quarter, and the company remains deeply unprofitable.

Facebook may be unpopular with teens, but it's still popular with adults, who have superior spending power and attract more attention from marketers. That's why Facebook's monthly active users rose 16% annually to 2.07 billion last quarter as its ad revenue jumped 49% -- indicating that it's still the 800-pound gorilla of the social media space.

Leo Sun has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Facebook. The Motley Fool has a disclosure policy.