I have lost my wallet.
'Portafoglio' — por-ta-FO-lyo. Four syllables; 'gl' before 'i' sounds like 'ly'. Stress on the third syllable.
Say this immediately when you discover your wallet is missing. Cancel your cards first (call your bank), then go to the police station to file a report.
'Portafoglio' literally means leaf-carrier (porta + foglio) — an old Italian term. The modern equivalent in British English is 'wallet'; American English: 'billfold'. Learning 'portafoglio' is also useful to know the expression 'fare il portalfoglio' — the hand gesture mimicking a thin wallet, meaning someone is frugal or broke.
Devo bloccare le carte subito.
I need to block my cards immediately.
Contact your bank immediately after losing your wallet.
C'è un ufficio oggetti smarriti?
Is there a lost and found?
If dropped in a public place, someone may have handed it in.
Avete trovato un portafoglio?
Have you found a wallet?
Ask at a nearby shop or venue where you last had it.
Italian banks have 24/7 card blocking services — the number is usually on the back of your card. If the card is gone, look up the bank's website. Alternatively, the universal Italian card blocking number is 800.151.616 (Banca d'Italia hotline for reporting lost/stolen cards).