I used to work with Boston University's online MSW and one of the things that they do is provide their online students with a list of approved organizations, agencies and hospitals that online students can connect with. They have a pretty high standard when it comes to that list but it is very extensive -- they do offer faculty support for the actual placement - and the bonus is the names of the agencies you get placed in really help your resume out too.
http://landing-onlinemsw.bu.edu/master/social-work?utm_source=mswcareers