If you didn't have an app or two on the device that could track it, or didn't sign for a tracking service, then to be honest, there really is no way to track it on your own.
You should call your service provider/carrier, either way, as they can turn off the service, keeping people from running up your bill. They may also be able to help you track it. But that is just a maybe.
It is important that you do change all your passwords for any account you accessed from that phone, so they can't access the accounts.
I am sorry you lost the photos of her. I hope your provider can help you. Good luck.