Abstract: Crowd simulation has been used in the entertainment industry to create populated environments that seem more realistic than isolated scenes, specially in urban areas. Video games are no exception, but the simulation of large crowds is often restrained by the remaining compute time available in CPUs, which is often used for most part of the game loop. This paper presents a parallel technique, using consumer grade graphics hardware, for proximity queries that is suitable for real-time crowd simulations. We use a truncated Voronoi diagram and a sampling technique, using ray marching, to find agents' neighbors in an environment texture. The experimental results suggest that our technique has significantly better performance than similar methods and can achieve simulations with thousands of agents in interactive frame rate.