How come when i track my iphone it keeps saying all devices offline?

Somebody stold my iphone about 2 hrs ago. I tried tracking down my iphone but it keeps saying all devices offline. How can i get my iphone back?

Added (1). Jimmy it didn't work for me but thanks

The device hasn't been used for a while or there's no signal. What i do is send a message to the phone and it automatically becomes online again.

It can't be tracked, if your cell phone carrier's website is experiencing any sort of problems.
First, call your cell phone carrier's customer service number. They can track it for you that
way, instead. You'll probably be asked if you want them to deactivate your line. I'd suggest
that you do that; and ask about the most economical way to get a replacement.