Usually when people use the word "empirically" it means they have some actual empirical evidence to bring to the table, not just random anecdotes.
If 40% of any segment of Facebook customers had substantially reduced their usage in the past year, that would indeed be unprecedented. I don't see a shred of evidence to support that supposition though.
It is what I saw in the past year, but you are right, I can't provide a completely verifiable and correct statistic to support my argument. Neither is it going to exist, because I don't think Facebook will ever state 'yes, we are going out of business'.
Must be hard to live your life based only on actual evidence all the time man. I can't imagine how much time do you invest verifying everything. Kudos for that.
[citation needed] (Even among teens Facebook's growth has not slowed much, let alone unprecedentedly.)