There is no systematic, filed way to find an insurance company by the policy number.

You can find a good qualified agent in any state that will be able to recognize most formats for the top insurance carriers.

If an agent is unable to help you determine a person's insurance company by their policy number, if that is all you have and not an insurance provider's name, you may be able to use the DMV to look up the policy number in their systems, which should have the insurance company.