YouTube was second with 15.3 million visitors, an increase of more than 3.5 million since 2015.
But Instagram and Pinterest, both primarily image-sharing sites, had shown much faster growth over recent years, Roy Morgan said, pointing out that Instagram had more than eight million visitors in an average four weeks, a rise of more than 5.6 million (238%) from 2015.
For Pinterest, the number of visitors was about 7.3 million, an increase of 4.6 million or 174.3% in the last four years.
The figures showed that Twitter now had 6.6 million visitors from Australia in an average four weeks, a rise of three million. The Microsoft-owned LinkedIn had 4.9 million visitors (up 1.4 million or 40.9%) while Reddit enjoyed the patronage of 2.9 million (up 1.2 million or 71%).
Facebook had strong representation among all five age groups: generations X, Z, and Y, baby boomers and pre-boomers. Among Generation Z, YouTube use was much more.
Roy Morgan chief executive Michele Levine said: "Although Instagram and Pinterest are undoubtedly the ‘hottest’ social networks in Australia for attracting new users, the two are attracting different audiences.
"Instagram appeals strongly to a younger audience with 68% of Generation Z and 52% of Generation Y using Instagram in an average four weeks. The two youngest generations are over 70% of Instagram’s total users.
“In contrast only 33% of Generation Z use Pinterest and the highest penetration of Pinterest users is found with Generation X of whom 40% use Pinterest. The majority of Pinterest’s users (53%) are in the three older generations of Pre-Boomers, Baby Boomers or Generation X."
Graphic: courtesy Roy Morgan