It can be very intimidating starting out as the Mobsters. While you do possess 5 cities they are so far apart that they will do you very little good.
Before doing anything, it is absolutely imperative that you make peace with everybody, especially the Bloods, Civilians, and the Police. Your first objective should be to turn all of your cities into strongholds (4-5 units at least in each city, more if you are on higher levels, such as Godfather or Kingpin.)
Once you have a nice strong defense, pick the weakest gang to be your victim. If there is no way to get to them you might want to consider making alliances with other civs. Pummel them as fast as possible because you can't afford a long war at this time in the game. Once you have destroyed them, rebuild your defenses in those areas--you must keep everything you gain safe!
See if you can't get an alliance with the police, if you can, then by all means do. Then steal their technology with a hooker (spy). If you're lucky they won't declare war on you, but if they do you have strong defenses. If you can't get an alliance with them, then pick another weak civ to destroy and go about doing it. Never attack the civilians if you are not already at war with the police! The civilians have an alliance with the police and if you can't handle the police at that time, attacking the weak civilians would be a fatal mistake.
Once you get a big enough force, go for the gold and hit the police with Terrorists and Hitmen and Gunships. You can field many more units than they can because your populace will not get unhappy about units away from the area. You will need all of your effort to topple to collosus but if you've made it this far that shouldn't be too hard for you.