I have lost my wallet.
'Portafoglio' = por-ta-FOL-yo. Four syllables. The double l is pronounced like English 'ly'.
The first thing to say when you realise your wallet is missing — to staff, police or a helper.
'Ho perso' is the passato prossimo of 'perdere' (to lose), the standard way to say something has been lost. 'Portafoglio' is the Italian word for wallet. In Italy, if you lose your wallet, you should report it to the nearest police station (Questura or Commissariato) and file a 'denuncia di smarrimento'. This document is essential for replacing identity cards and driving licences.
Mi hanno rubato il portafoglio.
My wallet has been stolen.
Use 'rubato' (stolen) rather than 'perso' (lost) if you suspect theft — different legal process.
Non trovo più il mio portafoglio.
I can't find my wallet anymore.
'Non trovare più' = can no longer find — used when uncertain whether lost or stolen.
Ho smarrito il portafoglio in metropolitana.
I lost my wallet on the metro.
'Smarrire' is more formal/literary than 'perdere', often used in official reports.
In Italy, lost property found by members of the public should be handed in to the Comune (municipal authorities) or police. The finder has no legal right to keep the property. Items handed in are held for one year — if unclaimed they may be donated to charity or auctioned by the municipality.