Can you reset an iPhone while its off?

Okay so I went to the mall a few hours ago and someone stole my f***ing iPhone and I'm pissed. I have a lock on it, and I already opened iCloud to track it but somebody turned it off, so every time I call it it automatically says "can't be reached." Now, it will notify when its turned on, but I'm scared that they can just take it home, plug it into their computer, and reset it, all while the phone is off. Is that possible or do they need the passcode? What should I do I've been crying nonstop over this crap.

Yes, that's exactly what they can do. The thief knows what he's doing. They power those things down the moment they steal them, then go home and reset them with the power off. Or they will do it from a laptop in their car from a random location, then drive home while it's resetting, so no one will ever be able to track the location.

They can also place the phone into a "black box" while resetting it, which does not all any radio waves to pass through, so the cell towers would never receive a signal from it to notify you that it's been turned on.

That iCloud app is essentially useless.

Hello i've recently ran into a problem my iphone 7 2 weeks after purchase all went black lagged before it turned off an nothing from it is it possible to wipe the device as once its wiped i can get a refund but just need to know where or how i can get this done. The Names mark