Online, there are only two category of states you can be in. You can either transmit visual-audio information (through commenting, posting, uploading, coding, etc.), or receive visual-audio information (reading, listening, watching, etc.).
That means that if you want to provide value online, you either change how people transmit or change how people receive. Or both.
Do this, and people will flock to that feature.
Example: Amazon's one-click purchasing changed how people order online by making the transmission process (entering ordering information) much, much quicker. Result? Increased sales for Amazon.
Another example: Facebook changed how people get information about the status of their friends by posting their friends' statuses on the home page (news feed), thereby reducing the time it took for people to find information on their friends.
Result? Users do most of their commenting, liking, updating on the home page.
These are simple examples, but very powerful ones. Online, you can't just focus on the content you provide. You have to focus on how your user is receiving the content or transmitting the content.
Make it easier, more accessible, more fun, more entertaining, etc. to receive or transmit content, and your users will flock to that feature.
In other words: control the mode of transmission or reception, and you control their activity.