Offline iPhone how to locate it

Start here:

Locate a device in Find My on iPad - Apple Support

Here is Apple’s advice for lost or stolen devices:

If your iPhone, iPad or iPod touch is lost or stolen – Apple Support

Use the Find My app to locate a lost or stolen device – Apple Support

If the Find My iPhone feature was enabled prior to it being “misplaced”, then if active, you would stand a good chance of locating it. 

However, if the feature was not activated prior to being misplaced - or the iPhone has been inactive for more than 24 hours, the last known location will not be available - and the opportunity to use technical means to recover the iPhone may have been lost.

Well, you could spend a hour reading through all the documents linked above and still not find the real answer, so we will try to keep things simple.

The phone is "Offline" for one of the reasons listed below.....possibly both.

1) The battery has run down

2) The phone does not have an Internet connection where it is currently located. (Thieves like to put stolen phones in a special bag that will not allow cell or wireless signals to reach the phone)

Nothing you can do about this, other than keep checking a few times each day to see if the status of the phone has changed

Watch out for scam emails and/or messages from "Apple" or "Apple Support" claiming that your phone has been found....and you just need to provide a bit more information so the phone can be returned to you.

This is a scam that is trying to trick you into providing personal information so the bad guys can get into your phone. Apple will never send a message like this.