I know the OpenSteer project, it seems to be a very efficient simulation package, so have luck for the job! It includes a great crowd or group movement simulation with path or leader following and flocking. I hope once I will understand those things
Of course, it is also ported to Unity, maybe it could help you but it is in C# (I haven't tested): http://arges-systems.com/blog/2011/05/02/unitysteer-2-2-released/ Links are at the end of the article.

( My personal future plan is to extend my tile based hierarchical pathfinder with this vehicle movement system used also in Company of Heroes: http://www.gamasutra.com/view/feature/131505/toward_more_realistic_pathfinding.php?print=1 )