There are two reasons why this may have happened:
1. In the app you've used the filters to hide sites of different categories - in the search menu (top left) you can toggle these filters, click 'show all' to turn all the pads back on
2. Your Premium membership has expired - oh no! Non-premium members only see aerodromes, aerial points of interest, and selected hotels and restaurants, as well as any pads they've added themselves. You'll have to go Premium again.
Pro-tip: Some of our promotional codes give you a free premium trial on registration - if you are relatively new to Helipaddy and suddenly find yourself with many fewer pads than you started with, you may just be experiencing case 2 above!