For anyone that has the patience to listen to a good long ramble, I offer my two cents (for as much as pennies are really worth these days).

There are a lot of theories as to where Tessa has gone. The general consensus, even from the people being nasty about it, is Tessa really seemed to care about HINABN and its fan base, so for her to have just stopped for this long without a word means something's happening/has happened.
Maybe it's illness, or burnout, or a death in the family, or whatever, but it's big.

The rest of this post is going to run off this assumption, which is likely correct but possibly not: major emotionally/physically taxing event.
I'm not saying anything of what I'm about to say excuses her silence; please read that sentence about fourteen times, commit it to memory. These aren't my opinions about who's right or wrong, what's fair or morally right or whatever. It's just a possible explanation I've yet to see that I think bears pondering, not just about Tessa but any time something along these lines happens in your life and someone/something that matters to you, to any extent or for any reason, is suddenly gone.

Regardless of cause, the one thing I've seen over all the various communities and forums is disappointment she hasn't been telling anyone what's going on. The two schools of thought seem to boil down to: "She's shy leave her alone" and "It's just common courtesy to tell people."
The answer is not necessarily so clean-cut.