Pete (Seeger) taught us all how to do it! He was the absolute master at getting an audience to learn and join in with him, even on completely unfamiliar songs, in 4-part harmony, and in languages they had never heard before! He did these concerts for over 70 years.
We (Annie Patterson & Peter Blood) have led hundreds of singalong concerts across the US, Canada, New Zealand, and the UK over the past 30 years in churches, Quaker meetinghouses, folk song societies, schools, camps, and at conferences and festivals. We lead these using Rise Up Singing or Rise Again.
There are many, many other musicians who also use audience participation as a major part of their concerts.