It is possible to participate in social media without ever posting anything. I don’t think I’ve ever seen statistics on users who frequently visit social media sites without ever posting, but I imagine they’re out there.
The fact that constantly impresses itself upon me, however, is how social media use generates an imperative to speak. One appears on social media chiefly by saying something. The shape which that “saying” takes varies, of course. We can speak on social media by posting words, images, or, more frequently, some combination of both. We can speak by linking. We can speak, as well, by liking, retweeting, sharing, etc. Our profiles speak, too, it’s true. But their static speech does not ordinarily generate engagement. No one speaks back to the static presence of an online profile. To exist on social media, to be taken into account, one must speak. Silence doesn’t signal, virtue or anything else for that matter. To remain silent on social media is an act of self-privation given that the social media self is constituted by our multi-modal loquaciousness.
I’m intrigued by how this imperative reorders the meaning of silence beyond the parameters social media. In putting it this way, of course, it immediately becomes apparent that defining the parameters of social media is no easy thing. Are its parameters to be drawn around our immediate engagement with the platform or rather by the times when a platform may easily capture our attention, say whenever I have a smartphone on me? Or, more broadly still, are the parameters of social media to be drawn so as to include any moment that is tinged by the existence of social media, the moment, for instance, that I interpret as social media fodder even if I cannot then access a platform?
However we decide to draw those lines, I wonder whether silence may not be construed as a defect in consequence of the habitual experience of the self generated by social media, an experience which tends to bind being and speaking tightly together.
The point of contrast, it seems to me, is the capacity of bodies in physical proximity to be for one another without also speaking. This capacity to be in silence is important and valuable. It may be most important and valuable in those moments when our words fail us—moments of profound emotional depth.
Silence, of course, need not be permanent. It is, rather, an incubator of thought and feeling, essential to the emergence of intellectual and emotional maturity. Without passing through silence, what we have to say may be vain, vacuous, and even harmful.
There is, as the writer of Ecclesiastes put it, “a time to keep silence, and a time to speak.” Wisdom consists of knowing how to tell the difference. Social media tempts us with folly of believing there is only ever a time to speak.
L.M. Sacasas 
I’m very interested in this line of thought. Coincidentally, I’ve been thinking a lot about how various senses of silence relate philosophically to our modern communications milieu.
In noting the multiple ways we “speak” on social media, I think you’re homed in on an important aspect. I’d only add that even the lurkers, as those who view without posting used to be called, now speak volumes to the algorithms, the data brokers and miners, the developers, and the companies that own the domains and networks. Even much of the visible sharing is now automated to the point that no user action is necessary. What Erving Goffman called “backstage,” that way we act when we feel we have privacy, is now often just mirage – the Truman Show.
Every act of looking at a phone or other device, every change in location data, every moment we linger or even forsake an available action constitutes another data point, and thus, a kind of speaking in this way. To algorithms and programs, it might be somewhat analogous to body language – communicative tells we don’t mean to give away, but which only the very practiced have learned to disguise or obfuscate, and them not without sacrifice.
For the rest of us, I wonder about the extent to which we can realistically take responsibility for this new kind speaking, and whether we can live with the consequences of not doing so.
As I recall from my days on E-mail mailing lists, there could easily be a ratio of something like twenty or even thirty non-posters for every active poster. I was one of only a half-dozen regular posters on one role-playing fiction list that had more than a hundred members at its peak. Silence is not just common, but is arguably the norm.
I believe that there are multitudes of people that relish conversation, but just don’t want to participate. Movies are one example, we as a collective love movies, yet we can’t participate. People read blogs but don’t participate. I don’t believe that they feel (to themselves at least) less of a participant as they follow along with other people’s comments, seeing or not in their own mind. It may never make it to the comment section, but they (again in their own mind) participate in their own way.