Courtney Keniston is mild-mannered around friends at Centennial High School in Circle Pines, so her bold statements on Facebook often surprise them.

For every benign "mmm, bacon and cinnamon rolls" post about breakfast, the 14-year-old offers her opinions about religion or relationships.

"When I feel really strongly about something," she said, "I'll post something about it."

Social media allow adolescents and teens to be expressive -- and in Courtney's case both she and her parents believe it is constructive.

But a recent study by the Girl Scouts found that isn't always the case when girls go online. Surveying 1,000 teen girls who use social media, the organization found those with low self-esteem were more likely to project themselves through Facebook, Twitter or MySpace in ways that didn't match their personalities.

Of these girls, 22 percent portrayed themselves through social media as "sexy" and 35 percent presented themselves as "crazy." One in three said their online persona doesn't match who they really are.

All girls were more likely to present themselves as funny or social and less likely to present themselves as smart or kind.

Trouble is, girls who try to boost their image in the virtual world suffer problems in the real world that they don't anticipate, said Sabrina Lee Sanchez, program implementation manager for Girls Scouts of the USA. Classmates might recognize exaggerations and use them as a source for teasing or bullying. Girls portraying themselves as sexually active or drinkers might be pressured into those activities.

"They may get 'called' on these alternative identities or false impressions, potentially putting themselves in risky situations," Sanchez said.

The Girls Scouts has increased training for its troops on social media, and just last month announced a program, called "It's Your Story -- Tell It," to boost girls' self-esteem. The initiative challenges girls to express themselves through media projects or art.

"We know from our research that girls increase their self-esteem by trying new things," Sanchez said.

Social media's influence on teen girls was reflected in last year's Minnesota Student Survey, which showed that 43 percent of ninth-grade girls spent at least 11 hours per school week texting or talking on the phone. One in five spent 11 hours or more per week on "online activities."

The girls in Courtney's troop are linked via Facebook. Her mother, Amy Jones, is troop leader and Facebook friends with the girls, as well.

The troop often discusses do's and don'ts of social media, but isn't perfect. One girl lost social media privileges when she created a secret Facebook page to which her parents didn't have access. Bad grades cost Becca Parker, 13, her cell phone, so she connects with her 519 Facebook friends only on computer.

At a troop meeting Thursday, the girls laughed over their Facebook habits -- from Courtney's habit of posting about food, to others' posts about breakups, to the "Facebook wars" that erupt publicly between friends.

Becca's sister, Kaitlyn, 16, said people have gone too far with mean comments about pictures she posted. (Survey findings show 68 percent of girls have been the subject of online gossip or bullying.)

Jones said that her daughter is responsible on Facebook, and that it helps her stay in touch with friends while shuttling between her divorced parents' homes. She wasn't surprised that other girls use the site to make up exotic identities.

"It's just that they can present themselves in the way they want to be seen," she said.

In patrolling Facebook, Jones said the girls seem more willing to share intimate thoughts while the boys post whatever will impress others. Even if the girls' thoughts are genuine, Jones worries that they could be used against them.

"Just because my daughter has 421 friends on Facebook, they're not all close friends," she said. "I wouldn't want all that put out there for the whole freshman class to see. I could see how putting something out there like that -- really personal feelings -- could come around and bite you later once it's gone through the grapevine."

Surveyed girls claimed an average of 351 Facebook friends; a majority said they had friends they'd never met.

Courtney Keniston only friends people she meets. Her network has grown through Girl Scout camps and other opportunities to meet scouts.

She has lost Facebook twice, because grounding means losing social media, as well. It's a sign of the times that the loss of social media is as potent a punishment as not being able to go to a friend's house, said her father, David Keniston.

The silver lining in the Girl Scout data is that -- in the end -- face-to-face relationships remain more meaningful, even among girls who tweet eight times a day.

"When I get mad at people, I might talk to them individually, but I never post anything publicly about it," Courtney said.

Jeremy Olson • 612-673-7744