The loss of a Swiss identity card or their theft must be indicated immediately after statement at the local police of the place of residence. An identity card by any misplacement is considered to be lost, either through theft, loss or total destruction. For the application of a replacement identity card wihtin the country or abroad a loss report of a Swiss or foreign police place must be given.
If the Swiss identity card has got lost during a passing stay abroad and no replacement identity card has been issued for the return journey in Switzerland , the loss must be announced to a Swiss police station after the return in Switzerland. Foreign Swisses and foreign Swiss who have lost a Swiss identity card abroad must announce the loss also to a Swiss, diplomatic or consular representation.
The loss of a Swiss identity card entails their invalidity. Therefore, a discovered Swiss identity card may not be refunded or reused. The identity card numbers of stolen or lost identity cards are written out to the search nationwide and internationally. Therefore, travelling with a Swiss identity card appeared again can have extremely unpleasant consequences.
Costs of a new identity card can be found here.