Dodgy Tunnel uses Everyplay to record and share video. This feature is supported on iOS devices running iOS 5 or later, and Android devices running Android OS 4.1 or later.
If your device meets this requirement, but a problem occurs while playing, Everyplay may disable itself automatically. If this happens, try un-installing and re-installing the game - this will reset your game's data and should bring the Share button back. Dodgy Tunnel relies on cloud saving, so your score should survive the re-install so long as you are signed in while playing.
We've done our best to test Dodgy Tunnel thoroughly before releasing it, but if you find one that's slipped through our net, please tell us about it at firstname.lastname@example.org.