Where are Microsoft Office for Mac My Templates stored? Where do Word for Mac and Powerpoint for Mac store user templates?
According to this page, and confirmed by experiment, the path has changed for Office 2016.  It is now ~/Library/Group Containers/UBF8T346G9.Office/User Content/Templates.  (This is what you see in the Finder: if you use Terminal the last two directories have ".localized" appended to their name, which Finder evidently suppresses).

Be aware that if you performed an upgrade of Office, you will still have the ~/Library/Application Support/Microsoft/Office/User Templates/My Templates directory, but Powerpoint, at least, won't look in that location.