Suzanne Choney,NBC News

(NBC) -- American teenagers have "waning enthusiasm" for Facebook, but they're still using the social network while upping their time spent on other social media sites like Twitter, Instagram, Snapchat and Tumblr, according to a new study.

The Facebook diss is because of the "increasing adult presence, people sharing excessively and stressful 'drama' " on the site, says the Pew Research Center's Internet & American Life Project. But teens "keep using" Facebook because "participation is an important part of overall teenage socializing."

Facebook takes a bit of umbrage at the finding, albeit politely."We are always focused on making Facebook a great experience; and we're gratified that more than 1 billion people, including enormous numbers of young people, are using Facebook to connect and share," a spokesman said in a statement to TODAY. "As we recently announced, 665 million people use Facebook daily, and over 750 million people are now accessing Facebook on mobile devices."

Indeed, 94 percent of teen social media users interviewed by Pew say they have a Facebook profile, and that it's the social media profile they use most often. But teens are starting to "diversify" their social media diet, says Pew in its report,"Teens, Social Media and Privacy."

More teens are starting to gravitate to Twitter; 24 percent of online teens use it, up from 16 percent in 2011, says Pew,but only 7 percent say it's the social media profile they use the most. Another 11 percent have an Instagram account, but only 3 percent says that is the social media profile they use most often. (Instagram was bought by Facebook last year.)

Pew notes that 70 percent of teenagers on Facebook are "friends" with their parents, and 76 percent are "friends" with their siblings. Contrary to what you might think, many of them aren't trying to hide what they share with family members by blocking information that's posted, the study found.

Only "18 percent say that they limit what certain friends can see on their profile," Pew said. "The vast majority (81 percent) say that all of their friends see the same thing on their profile. This approach also extends to parents; only 5 percent of teen Facebook users say they limit what their parents can see."

Teens are also relatively comfortable with managing their Facebook privacy settings, unlike many adults; 60 percent of teens say they keep their profiles private, and "most report high levels of confidence in their ability to manage their settings," Pew says.

The findings are based on a nationally representative phone survey of 802 teens, ages 12 to 17, done between July and September 2012.

Teens who use sites like Twitter and Instagram "reported feeling like they could better express themselves on these platforms, where they felt freed from the social expectations and constraints of Facebook," Pew says.

And they're not the only ones reacting to those "social expectations." Some adults, too, are gussying up photos and life experiences to match what they think followers will want to see or "like."