As in a Twitter status, or 'tweet'. It shouldn't be used to refer specifically to a status on Twitter, though.
It is a message, so mesaĝo. I don't see why it would need a specific new term.
I'd use "afiŝo" as not to mix up private messages and statuses.
If it's in reference to one's current state, "stato" should be fine. But if you want to include in its meaning that it's being posted you may also consider "statafiŝo".