iOS devices [non-jailbreak] anti-theft apps better than Find My iPhone
Apps on the App Store must obey the App Store guidelines and stay within their sandbox.


  2.5 Apps that use non-public APIs will be rejected
  2.6 Apps that read or write data outside its designated container area will be rejected


Apps aren't able to disable an iOS device's power off functionality as this is fundamental to the device and is not able to be manipulated by an app on the device restricted to the code that is downloaded with the app:


  2.8 Apps that install or launch other executable code will be rejected


Furthermore, doing things such as taking photos in the background is not permitted per the App Store guidelines:


  2.16 Multitasking Apps may only use background services for their intended purposes: VoIP, audio playback, location, task completion, local notifications, etc.


Therefore, such an app will not be found on the App Store.