You jerk the leaders and haul them away. Go hunt them down during the day, and throw them in jail for inciting a riot, destruction of property etc...
Identify anyone lighting a fire, throwing a rock, looting, in possession of property (you know what I mean) arrest them.
The city leadership needs to get tough and quit letting these mobs run amuck.
Don't initiate a curfew unless your going to enforce it.
