I've pondered on this and wonder if religion could be the answer. I say this as an atheist. But churches, typically already established well in these areas, could have the community structure combines with good social values and zeal/commitment, even fanaticism to see through what would likely be tough time initially to cleaning up areas.

Something along the lines of a Knights Templar where segment of a community devote themselves to the protection of people in the area. It might even give youth an alternative to avoid gangs as while jobs are scarce they can join a 'higher order' so have an alternative that provides purpose and a raise in self-status.

Note: I know nothing about these areas or problems really so approach this mental exercise from a position of ignorance and Hollywood.