Prophet (SAW)'s Prayers When something is lost

Recite:

اللَّهُمَّ رَادَّ الضَّالَّةِ وَهَادِي الضَّالَّةِ أَنْتَ تَهْدِي مِنَ الضَّلَالَةِ ارْدُدْ عَلَيَّ ضَالَّتِي بِقُدْرَتِكَ وَسُلْطَانِكَ فَإِنَّهَا مِنْ عَطَائِكَ وَفَضْلِكَ

"O Allah, the One who returns the lost, by Your power and awe return what I have lost, for surely I have received it as Your gift and favour (boon)". (Hisnul Hasin)