My iPhone was stolen. Who to contact if I have AppleCare?

AppleCare and AppleCare plus does not cover lost or stolen devices.

you would have to have purchased AppleCare plus with theft and loss coverage which includes a insurance policy.

If you purchased it, you need to file a claim with the insurance company:

File an iPhone Theft and Loss Claim - Official Apple Support

You can file a claim here - File an iPhone Theft and Loss Claim - Official Apple Support

Note that you need AppleCare+ (not the one-year AppleCare Limited Warranty) with Theft and Loss Coverage.