This document proposes a user-centric approach called MobiCrowd to improve location privacy in location-based services. MobiCrowd allows mobile users to collaborate by storing each other's location information and responding to queries, hiding users from the location server unless no collaborative peers have the requested information. An epidemic model is developed to analyze how parameters like query rates and data lifetime affect privacy. Results show MobiCrowd hides a high fraction of queries, significantly enhancing privacy, and implementation shows it is lightweight with negligible collaboration costs.