I think there are some quad-copter at the market those can find you from your smart phone. I don't know how accurate it is and how does it works? Is there a solution that I can build an android/ios application that quad-copter can find exactly the smart phone which has this app installed?
You can make an app that send the location of your phone, then you can use sensor fusion using Wi-Fi and IMU to enhance the precision. But to locate people, like spying you only need Kali Linux, a few exploitables, you don`t need a drone.
I understood you want to build a drone that follows you. There are some you can buy, but DIY is more fun.
This can be modified to do what you want using ROS.
Yes, you can make an app of your own which will enhance the drone to gives you the exact location of your mobile phone or any buddy you make the app available on their mobile phone, is just a pity you are not a professional in this line, I would have given you some tips which will help you out and if you seems it's hell of a work will help you make one