To get the audience to sing along you have to start with songs which have a good singalong chorus, something very simple that they learned in school. Also you have to have a responsive audience. You can 'feel' if they are going to sing and if they are not, then there is not much you can do about it.
I remember a Pete Seager show on TV once. He was in England I think. He had an audience of real stuffed shirts and they just weren't going to sing. He made a right fool of himself by keeping on at them, trying to get them to sing along. He should have dropped the issue after the first try.

Bert.