how can i track my offline iPhone?

If it’s offline you can’t track it. If you enabled Find My before it disappeared go to https://icloud.com/find, put it in Lost mode. Do not remove it from your account, ignore any messages saying it has been found (they are scams), and see this Apple support article—>If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Apple will not get involved.

It's written on the box.

Your carrier knows the IMEI # of the device connected to their network.

That won't do you any good, though, since you can't track it that way.

None.