Search is working for me in Sierra.
Option 1) With Calendar quit....go to your User's Library > Calendar folder
Delete
- Calendars/Calendar Cache
- Calendars/Calendar Cache-shm
- Calendars/Calendar Cache-shm
Reopen Calendar and test
Option 2) reindex your Spotlight cache files.
Open System Preferences > Spotlight
Under Privacy tab drag in Macintosh HD. You will get a warning. Select OK. Give it a couple of minutes to remove cache files, now remove Macintosh HD from Privacy.
Open Activity Monitor in Applications/Utilities. Under CPU you should see several processes named mdworker. This is Spotlight indexing your drive. Depending on the size of your drive this could take a few minutes to several hours.
Test to see if Spotlight is working.
Option 3) Boot into Recovery drive and run Disk Utility > First Aid.
Some users have had to reinstall Sierra to get things working properly. See other fixes for Sierra by Kappy
Boot into the Recovery Drive by holding down Command R when restarting.
Open Disk Utility
Run First Aid on your internal drive, Macintosh HD
Quit Disk Utility
Select Reinstall macOS
Depending on your internet connection this could take some time to download the installer. Connect via Ethernet if possible (You can reinstall Sierra over Sierra. This procedure is no different than installing one OS over another.
This process should not damage your data but it's always advised that you backup first.
Show User's Library
The User's Library folder is hidden by default. To unhide: Select the Finder in the Dock. Under Go in the Menu bar > hold down the Option key and you’ll see the Library.
Finding the User Library Folder
http://www.takecontrolbooks.com/resources/0167/site/chap11.html#FindingtheUserLi braryFolder