The plummeting cost of Bluetooth tags and the ubiquity of mobile devices are revolutionizing the traditional lost-and-found service. This paper presents SecureFind, a secure and privacy-preserving object-finding system via mobile crowdsourcing. In SecureFind, a unique Bluetooth tag is attached to every valuable object, and the owner of a lost object submits an object-finding request to many mobile users via the SecureFind service provider. Each mobile user involved searches his vicinity for the lost object on behalf of the object owner who can infer the location of his lost object based on the responses from mobile users. SecureFind is designed to ensure strong object security such that only the object owner can discover the location of his lost object as well as offering strong location privacy to mobile users involved. The high efficacy and efficiency of SecureFind are confirmed by extensive simulations. 2 subway and bus riders [2]. The predominant method for recovering lost objects is through a lost-and-found place, where lost objects are turned in and returned to their owners with proper identification. Many (if not most) lost objects, however, may not be found or turned in, and the object owner may not know which of the possibly many lost-and-found places he should resort to. The recovery rate for lost objects is thus very low. For instance, University of California Police reported only 19.3% of lost items recovered [2]. In addition, the recovery latency of this traditional method may be too long to be useful. As an example, by the time a lost object is found and turned in to an airport office, the object owner may have departed to a different city or country.The plummeting cost and ultra-low energy consumption of Bluetooth tags make them very promising to revolutionize the lost-and-found service. In contrast to RFID tags, Bluetooth tags can directly communicate with any mobile device with a Bluetooth tag or interface within a long communication range up to 160 ft. Besides, Bluetooth tags can be used continuously for oneyear without changing the battery [3], [4] by adopting the Bluetooth Low Energy (Bluetooth LE) technique, and they only cost several dollars which are often negligible in comparison with the value of lost objects. In the lost-and-found context, a cheap and miniature Bluetooth tag can be attached to every valuable object and contain its owner's identification information. Once finding his object missing, the owner can use his mobile device to search for the corresponding tag. If the tag gets queried, it can report its location or sound an alert to be located. There are growing commercial Bluetooth-based products for locating personal assets, such as Tile [3], BlueBee [5], and StickNFind [4]. These attractive products, however, often require that a lost object be sufficiently close to the searching device. For example, BlueBee tags [5] and StickNFind tags [4] support up to 160 ft and 100 ft, respectively. This inherent range limitation makes it infeasible to recover the lost objects far away...