There is no way to know it unless you had it written down, saved the box it came in, etc. And also, you cannot locate a phone via that info. You would need to have either had an app on the phone that is for tracking, or have signed up for a tracking service.
You can try contacting your carrier/service provider as they 'may' be able to help locate it. They can also turn off the service for you, so no one runs up your bill.
Also, you should really change all your account log ins and passwords to any account you accessed from the phone. Before someone else accesses them.