Assuming you used google to backup your photos, any backed up content would appear on photos.google.com

In addition, try using android device manager to locate your phone if possible. Or at least lock it. https://www.google.com/android/devicemanager?hl=en_GB&u=0

Assuming you used Google to backup your photos, any backed up content would appear on Google Photos.

In addition, try using Android Device Manager to locate your phone, if possible. Or at least lock it.