Social Worker Anzsco code 272511 assessing body AASW, is currently on the SOL1 list, which means you just need at least 60 points to get an invite and you don't have to be sponsored by a state..
If you have at least 3 years work exp as a social worker you claim 5 pts, but 5 years claims 10 pts.
all this depends on whether your occupation will still exist in 3 or 5 years time and is still on the SOL1 (189 independent PR visa).
Have you gone through the skillselect website for more info?
I'm not going thru the 189 route, because my occupation falls under the 190 route which means I need a state to sponsor me.