A thread is what you started when you put up your post and I'm continuing that thread by responding.
It's unusual for them all to disappear. When you tap the Contacts icon, you should see headings of Phone, Groups, Favourites and Contacts. If any of the first three has a blue background and you don't have any contacts stored under that category, you won't see any. Make sure the Contacts heading is the only one with that blue background.
If it's not that simple, use your PC to log into G-Mail at your local Google website. You may find they kept a copy of your list in there.