Run updatedb first. You can run it manually from the command line.
updatedb
It should have scheduled itself as a cron job when you installed slocate. If you just installed slocate, it will not have run yet. Otherwise, make sure you have a cron daemon running and that there is an updatedb task scheduled. Also, make sure your computer is on when it it is scheduled
If this is a VM and does not run continuously especially never spent days on this will happen. Just in case check the cron job found here:
The cron job is found here:
/etc/cron.daily/mlocate.cron
Thats’ pretty much it.