Review on Improved Joystick Thumb Stick Key Caps for enhanced gaming experience on Sony PlayStation: Hapurs Anti-skip Silicone Replacement Joy Stick Controller Shell Cover Protector for PlayStation 3, PS4, and Xbox 360 by Anurag Case

If you're missing the entire thumb pad, even the bottom, it won't work without modifying the adhesive or enlarging the plastic part on the controller. Also, they tend to slip even on one that hasn't been peeled off and end up slipping off immediately. Which usually happens at a very inconvenient time. They're inexpensive though, here's the thing.