Social media is about being social. It is about connecting with your communities: customers, employees, partners, investors, service providers. It is about conversations and collaboration between these communities. You are not social if you are not having a dialog. Remember, monologues were never considered social.
Social media is also about using media to be social. In the very near past (and even today), conventional channels of media were more unidirectional and slow for two way communication. Communities are now conversing using the new media in form of various social network site. People are blogging and commenting everywhere. Use these multitude of media to connect with them and start a conversation.
Devices these days have made media ubiquitous and your communities are having conversations everywhere and at all times. You need to be available 24x7 to connect with the communities.