Activate face recognition in the new Google Photos
I just found the solution to this. All you need to do is:


Connect to a USA server via a VPN 
Clear the data and cache of the Google Photos app. 
Open the app again and activate the "Group similar faces" in the settings
Check back the search menu after a couple of minutes and the faces would be there. Google already did the recognition for you, but kept it for itself.
Disconnect from the VPN.