Torvalds. David Brin. Tim O'Reilly (although Tim uses or used to use multiple platforms in an ongoing fashion). Randall Schwartz. A few others I'm not thinking of right now.
Plus garnered a bit of a "tech"/thinker corner. I don't know whether it has any remaining vibrancy/growth, at this point, or whether its mostly a matter of inertia combined with the crapitude of other platforms for the particular communicating they are doing.
Too bad Plus was so thoroughly hosed from the start by political agendas.
OT: At Christmas, I stopped accessing Facebook. I thought it would be for a few days or a week. Coming up on two months, soon, and I haven't been able to make myself go back. Even with a relatively small set of FB friends whom I actually, personally know, and who are nice and not rabid and actually respond meaningfully to some of my own contributions, there.
In some ways, the impersonal, more technical content on Plus (and here, and etc.) is easier. There is no "missing aspect" as there is with FB engagement with friends.
Twitter? Gave up on that years ago. Tim O'Reilly had an interesting post or two about some of its positive, community aspects, in its early days. But now, it just mostly seems a megaphone for the loud and discontent.
And then, too, anywhere Trump et al. are and that seems to aid his lying megalomania. I'm not inclined to lend it the (incremental) support of my participation.
If he's a particular indication of their future, well, then, welcome to the gutter, Twitter.