Opening your wallet to a zero balance is heart-stopping, but more often than not the funds are perfectly safe and simply not being displayed. Working through the usual causes calmly is the first step.
The most common reason is looking at the wrong network. Many wallets support several blockchains, and if the app is set to a different network than the one your funds are on, it will show nothing. Switching to the correct network usually makes them reappear. A similar issue is having the wrong account selected within the same wallet.
Other simple causes include an app that has not finished syncing, needing a refresh, or holding a custom token the wallet has not automatically detected and needs adding manually.
Before assuming the worst, check the address on a public block explorer. If your funds show there, they are safe and the problem is only in how the app is displaying them. Genuine theft is far less common than a simple display or network mix-up.
