Spotlight doesn't work after Yosemite Upgrade
Spotlight: How to re-index folders or volumes
Learn how to re-index a folder or an entire volume for Spotlight.

From the Apple () menu, choose System Preferences.
Click Spotlight.
Click the Privacy tab.
Drag a folder or an entire volume (your hard drive) to the list.
If prompted for confirmation, click OK.
Remove the item or volume you just added to the list by clicking it and then clicking the minus ("-") button.
Close Spotlight preferences.
Spotlight will re-index the contents of the folder or volume.