Mary Madden, senior research specialist at the Pew Research Center's Internet and & American Life Project, said 72 percent of millennials use social networking sites, compared with 40 percent of adults 30 or older.*

She said young people share personal information about themselves, whether it is their birth date, phone number or a picture from a party, as a way to nourish relationships.

"You are trading information about yourself as a form of cultural currency," Madden said. "By posting a photo or an update about what you did at a bar last night, you are sharing with friends to initiate an exchange and continue a friendship."

Problems arise, she said, when the information is misused.

"It's an interesting balance they have to strike in deciding how much to share in order to initiate or maintain a relationship but not overshare with their network," she said.

Madden pointed to studies that show most people can be identified with three pieces of information: their sex, Zip code and date of birth. And seemingly anonymous profiles that catalogue preferences, such as movie lists on Netflix, can also be used to identify users.

* Note: This article originally stated that 72% of millennials and 40% of adults 30 and older use social networking sites daily. These numbers refer to overall usage, not daily usage.

Read More