Every social media employee? I would guess most have separate personal accounts and accounts used to manage their company's pages.
Historically, some brands did create full Facebook accounts, but Facebook now discourages that and as far as I know most brands are using Pages now. For a while Zuck's dog, Beast, was a notable exception (he had a Facebook account long after that was discouraged) but it looks like he's just got a Page now.
(I used to work at Facebook.)