First, don't panic.
We advise you to "freeze the card" so you have time to look for it. Go to the main page, then in the tab spending and activate the "freeze card" option. If later on you find the card, you can undo the "freeze".
If the card is really lost or even stolen, you can report it. Go to the main page then in the tab spending and click on "card info".
Attention! Reporting the card as lost or stolen will deactivate it. You won't be able to re-link the card if you find it.