In looking at social media and libraries I found most libraries are using Facebook & Twitter, some of the bigger ones are using Pinterest & Instagram too. The library at the University of Melbourne has a strong Twitter account with many tweets during each day till 5pm when the tweeter signs off for the day. The tweets are about info form the libraries collection, exam help, new additions to the collection. The State Library on their Twitter feed and Facebook also do the same but what I liked was all the articles posted re what really goes on behind the scenes at the state library;
As the State Library also hold an enormous archival collection, displaying them worldwide via social media is fantastic, on all their social media account they are actively doing this.
Libraries loving social media;
Frankston Library @frankstonlib
Moonee Valley Libraries on Pinterest
Library at the dock on Facebook