Q: ios9.2.1 searching problem

First, try restarting the phone by holding down the Home and Power button until you see the Apple logo. If that doesn't work, go to Settings > General > Spotlight Search. From here, you can turn Siri Suggestions on or off and choose which apps to include in your searches. Make sure all of them are turned on.

Use Search on your iPhone, iPad, or iPod touch - Apple Support

same issue here. I disabled all options for spotlight search restarted the phone, but frequently the search is not showing the apps when I search for them.

I Also had this problem on my 6s Plus. It was very frustrating because I have so many apps and use both an ipad pro and the iphone, and apps are not always in the same folders on the two devices. Searching for them by gliding one's finger down the centre of the screen to open the search tool has become a necessity.

powering off the device and back on fixed it. Thanks!