Welcome to the community!
Sorry to hear you got your phone stolen. You should report the theft to your local police department.
Did you try calling it to see if anyone would answer?
Is it an Apple or Android phone? If its an Apple phone do you have the find my iPhone app installed and activated? If you do have in enabled you can trying using to see if you can located the phone you can get more info here.
If you have an Android phone and have find my device turned on you can also try locating your device through Google you can get more info here.
If you are not sure if you had those features turned on you can still try locating the device in the event it was activated.
You can also report the device lost to Fido and they can blacklist the device so it will not be able to work on any carrier in North America.
If you will try to locate the device though you should not blacklist the phone or disconnect your service because you will still need the phone to be active in order to locate it. You can have Fido block all out going calls so no one can use it to make calls.
Always take caution if you are successful in locating the phone, don't approach the person by yourself or you can consider calling the police and have an officer approach the person.