ClickSearch is probably the most convenient tool and the most affordable way I've used to track someone's whereabouts. I simply enter the person's full name on the search bar and wait for the results. The reports are amazingly thorough and very helpful. It's great for tracking down long-lost friends, colleagues, and even estranged family members.
Aside from it's compatible with various devices, TurboSpy is super easy to install. Unlike other spy apps, I was able to start using this great app even without rooting the device I wanted to monitor. And it only took me like a couple minutes.