Here is a nice a starter UI kit for Sketch for getting started with a VPN mobile apps. Kit includes 14 mobile templates which could be easily customized for your own projects with just a few click.
The UI kit contains an universal, fresh style which fits to emerging trends in mobile interfaces. Bolder headlines, bright colors, simpler more universal icons combined with light design and thoughtful UX will allow you to get inspired and create your own unique product. As all the objects are created using shapes.
This set would be a great match for your app!
It will definitely save your time and energy.
14 SKETCH Files
100% scalable Vectors
Totally based on Flat Design Standards
Fully Layered & Organized with proper Names
Easy to change color style
Well-documented Help file