This paper presents an IoT platform for Smart Cities designed for the integration of security agentsin the task of locating vehicles of interest through license plate recognition and queries to external databases. The platform is composed by an Android application capable of performing real time license plate recognitionand a server executing a RESTful API designed to query external databases and integrate the application users. The adopted recognition method uses the text recognizer implemented in the Mobile Vision API by Google, and specific heuristics for results adequacy and refinement. Experiments were conducted considering four situations of movement of the users with respect to the vehicles in the field of view, represented by photographs and frames from video streams recorded in real open urban scenarios, revealing 86.6% of average accuracy. The phases oflicense plate recognition in the smartphone, communication with the API and notification of the interested users showed satisfactory efficiency, demonstrating the feasibility of the platform concept.