How can we (local neighborhood watch) take action against a landlord that has disruptive, criminal, drug dealing tenants?

Call the police, take video or photos of any illegal activity. If you are a tenant of the building, there are procedures to force the landlord to bring eviction proceedings against the illegal activity and if the landlord does not after proper notice to the landlord you would have the right to bring a proceeding against the offending tenant. You should discuss this situation with a NY landlord tenant attorney to examine all your options.   Walter Jennings,Esq. Landlord/Tenant Attorney