Do you have Photo Stream enabled on your Mac and was it enabled on the iPhone? If so then make sure iPhoto's Photo Stream preferences are set as shown in this screenshot:
Also you might want to lock, i.e. set the phone into Lost Mode, or erase your cell phone from the iCloud.com/Find My iPhone site (if you have Find My iPhone activated on the iPhone)
However, these functions must have been enabled on the iPhone prior to it's being stolen.