CodeIgniter as a mobile backend

Hello, everyone. I am new to CodeIgniter (and for that matter PHP), but I have experience in Node and mobile development, and had a few questions regarding CodeIgniter.

I was wondering how well CodeIgniter does for mobile backends. The reason I ask is because I recently saw an app builder that used CI to power the backend for native Android and iOS apps. Does anyone have any experience using CI for this purpose? Do you think it is a good fit?

Apart from that, I have a few general questions regarding the framework;

1. Does CI work well on PHP7 or the HHVM?
   
2. How active is  CodeIgniter development and the community?
   
3. How does CI stack up against frameworks like Symphony and Laravel?