There's a BBC article that explains all this and focuses on a jolly nice police person called Ed. He is not, as far as I am aware, a duck. Which is good.
"Posting a message on Twitter warning about a spate of burglaries in an area is a similar concept to pinning up a poster on the local parish council noticeboard."Almost certainly useful for Jan10 exam.
"Doing either in isolation might be fine, but by doing both we can spread that warning even further."
Greater Manchester police have been signing up users to get Facebook updates on crime in their area. More than 25,000 people seem to have signed up. Sign up! Get the updates!
Some of the links from these articles might be handy to take a look at as well.