If your keys get stolen or go missing the first things you need to do is call a locksmith and have your locks changed or rekeyed straight away. Especially if the keys have anything that could link the thief to your address.
Don’t take any chances and certainly don’t leave the house unattended until you have had all the locks changed.
Remember, in the event of a theft from your premises and there is no signs of a forced entry it’s very unlikely that you will be covered by your insurance policy.