How do I lock my stolen iPhone?

1. If your iPhone, iPad, or iPod touch is lost or stolen - Apple ...
2. Find the serial number or IMEI on your iPhone, iPad, or iPod ...

You may use a web browser to get the Serial Number and the IMEI Number. You cannot track using the IMEI number. but you may need it so keep it handy

Log in to https://appleid.apple.com with your Apple ID credentials. All your devices will be listed there. Click on any to get the details.

Don'ts

If you remove the device from your account after you erase it, Activation Lock will be turned off. This allows another person to turn on and use your device.

Do's

• Mark As Lost.
• Erase your device.

You are addressing this to another user and not to Apple in this forum.

Apple Support Community Forum

This is Apple Support Community forum, primarily for a user to user interaction for information & idea sharing between users, if need be, extend support on technical know-how in handling Apple products from a more experienced fellow user, This is not the right forum to discuss with Apple Inc.

Did you enable Find My?

If you didn't turn on Find My [device] before your device was lost or stolen, it can't be used to locate your device nor you can use the IMEI number for tracking the device.

The best action would be to Change your Apple ID password and change the passwords for other internet accounts on your device. This can include email accounts, Facebook, or Twitter, etc...

Please understand this is a public forum: While attaching a Screenshot, do not provide any personal credentials, such as Card detail, email id, apple id, IMEI number, Serial Number, Phone number, Order ID, if you are sharing a map ensure your location is not identifiable, etc.