LIZ PEEK: The infuriating invisibility of Facebook COO Sheryl Sandberg.

Where is Facebook’s Chief Operating Officer Sheryl Sandberg? The alleged “adult in the room” has been nearly missing in action since the Cambridge Analytica scandal broke on March 17.

To date she has offered up only one measly post, which echoed CEO Mark Zuckerberg’s explanation of what went wrong, and one interview on CNBC.

For a woman known as a great communicator, not to mention the company’s critical No. 2 in command, credited with building the very advertising model that has got Facebook in hot water, Sandberg’s reticence is not only mystifying but also inexcusable.

It was former Google CEO Eric Schmidt who dismissed privacy concerns with a blithe, “If you have something that you don’t want anyone to know, maybe you shouldn’t be doing it in the first place.”

Back in 2009, Schmidt’s statement was creepy and offensive. But now that the big networking firms are the ones being exposed, it’s full of schadenfreudeliciousness.