I do not necessarily think you need to find another source that uses the term "age of social media."  You can make that YOUR name, and then include a citation that clarifies.  The link below would work, I think.  The Pew Research Center is very well respected and the link makes clear how completely social media has become part of modern life.

http://www.pewinternet.org/fact-sheets/social-networking-fact-sheet/

We argue that we are Beyond New Media, and are now in an age of polymedia 

Polymediation is that next place we need to get to, where scholars, practitioners, and (most importantly) users begin to have their realities (the plural is necessary here) shaped by their converged mediated moments. With this premise in mind, we offer the following thoughts on a working definition of polymediation:

Polymediation is both the process and product resulting from media producers - who can be everyone and anyone with access – existing within a converged media state. Polymediation, as a term, acts as a discursive entry point to allow for the conversation about what is happening at the intersection of media convergence, content creation, gatekeeping, narrowcasting, online identity, social networks, etc. Polymediation moves beyond media convergence alone, by examining the simultaneous processes and outcomes of convergence and fragmentation. Polymediation can be used as a verb, a noun, an adjective, and an adverb. Through actions the phenomena change leaving us to simultaneously act as producers, audiences, and critics who can describe, react, examine, and assess the implications of ongoing discourses and technological advances.We understand there is a relationship between the technological artifacts or tools (smart phone, laptop, etc.), the various sites of mediated communication (Facebook, Twitter, Snapchat, FaceTime, etc.), and the processes of communication, that help define our relationships with each.

http://www.amazon.com/Beyond-New-Media-Discourse-Polymediated/dp/0739191020

Have look at New Media and Society, there are probably a number of papers published in this journal. It is a gold mine for social media research.

Thank you very much for your valuable comments. It seems there are multiple terms and theories for defining  commucation in this age. "Network society", "Digital mass media", "Social media", "New media", and thanks to Andrew :) "polymediated communication" etc.  I will check the resources you have kindly suggested.

At the beginning, I was hoping to write "We are in the age of social media. The proliferation of social media platforms provides public sector organizations with novel ways of interacting with the citizens and managing informal networks within their own organizations. So, the students of public administration (and public administrators as well) must learn how to understand and use the untamed social media in order to enhance public services, and organizational life."  

This seemed easy to say. However,  although social media has become a part of our daily lives (at least some of ours), neither the people nor the public organizations are willing to engage each other in social media.For example, I am working on a study about how local governments use social media for public relations purposes, and it seems like almost every municipality has one or two social media accounts. But they use social media for self-expression only, with limited interactivity (or marketing maybe), and the local community has little interest in following those accounts.

I think this is more than a lack of interest in politics. As many examples show, social media can be quiet political. When we scratch the surface, we see a conflict between two nods of power: "social power" versus "public power" (I mean the power which is used by public organizations) which enjoy expressing themselves freely in their own domains. So, why would anyone/public employee confine himself/herself with the rules defined by some "administrator" and in some cases,risk criminal or disciplinary punishment, or why would a public organization allow citizens or employees to expose things on social media which would otherwise be kept safely under control? And, after all, what is it that the students of public administration should learn about social media?

I think you should look up technological determinism theory. It explains the use of emerging or new technologies for communication. If organisations switch from the use of bulletin and other old media to social media, it is due to the advantage that social media has over the old communication media. This theory can also be supported by medium theory by Marshall McLuhan.  

Thank you Tope. Then we can talk about a trade off between advantages and sacrifices. To what extend the citizens would be willing to sacrifice their freedom of self expression to interact with the public organizations and to what extend the public organizations would be willing to sacrifice their control, regulation power, and secrecy to interact with the citizens? I can figure the advantages, but currently (in my country at least), it seems the disadvantages overweight the advantages since the two sides often confront rather than co-operate. I don't know if that's the case in other settings. 

Maybe you should take into account social comparison theory or social capital theory. They can help you to explain why people communicate via social media.

Dear colleague,

I think that books and texts of Manuel Castells and Shel Holts are appropriate, regarding your question.