The typical teenager has 300 Facebook friends and 79 Twitter followers, the Pew Internet and American Life project found in its report, Teens, Social Media, and Privacy.
And some have many more.
The 2013 study also says the norms around privacy are changing, and the majority of teens post photos and personal information about themselves for all their on-line contacts to see.
More recent survey data released last week by the Canadian non-profit digital literacy group MediaSmarts shows Canadian youth do take some steps to protect their privacy - for example, by not posting their contact information on social media.
But the paper, Online Privacy, Online Publicity, also points out that most kids have only a limited understanding of things such as privacy policies, geo-location services and the implications of sharing their passwords.
The research contributes to an emerging picture of how teens' ideas about friendship and intimacy have been altered by their immersion in the on-line world, says Patricia Greenfield, a UCLA developmental psychologist and the director of the Children's Digital Media Center @ LosAngeles.
In her own research, Greenfield has found that young people feel socially supported by having large networks of on-line friends, and these are not necessarily friends they ever see face-to-face.
"We found in our study that people, college students, are not getting a sense of social support from being on the phone. They're getting social support through bigger networks and having a sense that their audience is large."
The result is a decline in intimate friendships, Greenfield says. Instead, many young people now derive personal support and affirmation from "likes" and feedback to their postings.
"The whole idea of behind intimacy is self-disclosure. Now they're doing self-disclosure to an audience of hundreds."
Other research at UCLA shows teens' increasingly preferred mode of communication with their friends, texting, makes them feel less connected and bonded than face-to-face communication.
Graduate student Lauren Sherman studied various forms of communication between pairs of friends. She found the closer the experience was to in-person conversation, the more emotionally connected the friends felt. For example, video chat rated higher than a phone call, but the phone created a closer connection than texting.
"I don't think digital communication in itself is a bad thing," said Sherman, "but if we're losing out on opportunities to connect with people as well as we can, that's a problem."
Studies have estimated teens typically send more than 3,000 texts a month.
Greenfield says that indicates kids are opting for efficiency of connection over intimacy.
Also on HuffPost