If your NIE has been stolen, the first thing you should do is file a police report with the Mossos d’Esquadra via the link below. Filing a report assures that you will not be held accountable if someone else uses them.
In the event of loss, you don’t need to file a report, but you do need to notify the police.
The next step is to request a duplicate of your NIE, you can do this by making an appointment online and completing the ‘Loss or subtraction of document’ form via the link below.
After you have submitted all the required documents at your appointment, it can take a maximum of 40 days for the immigration office to send you your duplicate NIE. Bear in mind that you only have 30 days to request the duplicate after the moment in which your NIE is stolen or goes missing.