so how can i find my phone while it is switched off?
The phone is not going to show up if it has been powered off, the battery has run down or the phone does not have an Internet connection where it is located.
Sometimes, a "Last Known Location" will appear for a day or so after the phone has become offline.
Not really anything else that you can do at this point, except keep trying.
I'm sorry, but a tiny fraction of phones that are stolen are ever recovered, so you will need to keep your expectations on the very low side.
If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support
Be very careful if you receive a message from "Apple" or "Apple Service", etc notifying you that the phone has been found and you just need to "provide a few more details" so the phone can be returned to you. Apple will never send a message like this. Things like this are always scams that are trying to trick you into revealing personal information, your Apple ID, Password, etc so the bad guys can get into the phone.