To start with, let's clarify a definition:
Community policing is a philosophy that promotes organizational strategies that support the systematic use of partnerships and problem-solving techniques, which proactively address the immediate conditions that give rise to public safety issues such as crime, social disorder, and fear of crime.
Challenges to making this system work start with building effective partnerships and insuring supportive involvement by all the needed parties. If businesses or individuals are apathetic or afraid to take part due to fear of reprisal, the level of self-policing that is necessary to make community policing effective is compromised. Once adequate involvement is obtained, training is the next step so that all parties understand their role and the procedures that need to be followed to ensure safety and effective communications among everyone involved.
Unfortunately, one major block to effective community policing may become an overwhelming amount of criminal activity in the given area. If the severity of problems goes beyond what members of the public can handle, the community may have to be policed by more formal authorities with a harsher set of enforcement tools and consequences available.