Virtual Community Attraction
From the abstract:
"Theories of broader Internet use have indicated both entertainment and searching for friendship as motivational forces. This exploratory study empirically examines the importance of these reasons in assessing why people come to virtual communities by directly asking virtual community members why they joined.
The responses to the open-ended question “Why did you join?” were categorized based upon the reasons suggested in the literature. Across 27 communities in 5 different broad types, 569 different reasons from 399 people indicated that most sought either friendship or exchange of information, and a markedly lower percent sought social support or recreation. The reasons were significantly dependent on the grouping of the communities into types. In all the community types information exchange was the most popular reason for joining. Thereafter, however, the reason varied depending on community type. Social support was the second most popular reason for members in communities with health/wellness and professional/occupational topics, but friendship was the second most popular reason among members in communities dealing with personal interests/hobbies, pets, or recreation."
What's still missing here to answer the question (of whether people online are different from people not online) is a comparison to a similar group of offline folks.