How many social media are they? Many. However, how many? Who uses them? The first set of questions could be approached if we just visit the Wikipedia “social networking websites” entry. While, the "Add this" share button, which can be found in the footer of this page, reveals more than 280 options. The number of this list presented there could be well surpassed, though, if we add to the count all the existing virtual communities. The final number may be infinite. Further, who uses them? A public, of course. See, Social Networking Fact Sheet, http://www.pewinternet.org/fact-sheets/social-networking-fact-sheet, for instance.
The same variety of social media platforms is an indicator of the variety of audiences. Otherwise, there would be no need for another social network or a virtual community.
"Social media" is to be regarded, here, a rather generic term; unifying a variety media, technologies and, mainly, audiences. Just as Antiquity had been regarded before Lessing. Different means of expression have different expression abilities and qualities. By the phrase “Facebook is not Twitter, and Twitter is not Facebook”, I understand that the audience of Facebook is different from the Twitter one.
And, what about art history?
It goes without saying that all the above statements encompass art history public as a public. Paraphrasing, the art history audience of Facebook is different from the Twitter one. How is it different? It differs, first of all, by its choice to use each means. Further quantitative and qualitative research on this matter could produce more secure responses.
Nevertheless, apart from using social media as a means of art history communication, teaching and diffusion of research, art history studies have already appeared, indeed, a) discussing particular social media (Facebook, Twitter and Instagram, for instance) art history, its methodology and digital research tools, or b) using these social media to approach history. Yet, where these papers get published? Are these papers and studies considered to be acceptable in terms of the Research Excellence Framework (REF) or when applying for a tenure track position? Just some thoughts.