dear sir my Phone stolen but find my phone is off what can i do? thank you

Don'ts

If the device is removed from an account after it is erased, Activation Lock will be turned off. This allows another person to turn on and use the device.

An example of my iPhone 5 is given in the GIF below. There is no "Undo" after you remove it from your account.

Was Find My enabled?

Open the Find My app. Choose the Devices tab or the Items tab. Select your missing device or item, then choose Play Sound. If your device is offline, it won't play a sound until it connects to a network.

Use the Find My app to locate a missing device or item

If Find My [device] was not turned ON before your device was lost or stolen, it can't be used to locate a device nor one can use the IMEI number for tracking a device. The best action would be to Change the Apple ID password and change the passwords for other internet accounts that were used on the device. This can include email accounts, Facebook, Twitter, etc...