From Facebook to the photo-sharing site Pinterest to virtual adventure games, software that helps people meet, converse, work and compete with others is drawing billions online. The use of social media comes with a price, however. Every photo upload or click of a “like” button deposits users' personal data online, much of which is sold to help businesses target advertising. To some, such data mining endangers long-cherished privacy rights, but social media supporters say it is a small price to pay for the benefits of online socializing. Meanwhile, critics of social media express concern that many members of the digital generation may fail to develop vital communication skills because they prefer virtual contact over face-to-face conversations. But proponents say most people use social media not to avoid others but to stay in touch with them.