Outlook 2016 additional search fields have disappeared
Solution 1:
Select Search Box, navigate to Refine Tab, click 'More, add the search criteria to the search box.
Solution 2:
In Outlook, in the grey area at the top, right click, customize, and then in the dialog box that comes up, All icons, select Search and add it
Now in my Outlook I use the Search field at the top of the of the email messages. I click there and that shows the the Search tab with all the search tools including Advanced Find.
I prefer the latter approach and it is all there.