You can also use POP (Prototyping on Paper), https://popapp.in/
POP is specially focused on develop mobile app wireframes, it is very simple to use. After finishing your paper sketches, you can upload them via mobile and edit them on your desktop with a bigger screen. Every change you make can be showed on different devices simultaneously so you can discuss with your team by commenting on the mock-up anytime.
We used to do paper based prototyping in our sprints earlier, where I would just try to act like a mobile and will change the paper on a touch/interaction of the user testing the sketch usability. With the advent of this the paper based usability testing has been taken to a whole new level.