When your audience shares the content you provide, they are seeking social status. If you're not providing information that will make them look good, they aren't going to share it. 

Investor Press Release: New York Times Company, 2011-Jul-13

Sharing as Information Management – With more content, more sources and more people to share with, many users find sharing is a useful way of managing information. 85% of respondents said that reading other people's responses helps them understand and process information and events. 73% said they process information more deeply, thoroughly and thoughtfully when they share it.

Motivations for Sharing – The study identifies five primary motivations for sharing. Each of the five motivations has a common theme: sharing is motivated by the relationships users have with one another. Therefore, marketers should be focused on providing content that enhances consumers' relationships with one another.

Personas – The study identifies six sharing personas. Each persona is defined by emotional motivations, desired presentation of self, role of sharing in their life, and the value of being first to share.