Libraries have approached social media in all manner of different ways, some libraries branch out over Facebook, Twitter, Instagram, Flickr and many more. Social media is a great tool for libraries to use it makes the costumes aware of times and any important dates coming up, it can also share activities that have been taking place at the library.
Here are some links I have found that connect to different libraries and their different social media accounts:
Here is the State Library of Victoria's social media page for Facebook and it contains a large amount of promotional advertisement for their current exhibitions.
State Library of Victoria

Here is the Moonee Valley Library's Pinterest account, they have used this image based social media tool to great boards that include things such as 'Best 100 Reads for Young Adults' or 'Local History Collection'.
Moonee Valley Library

Here is the National Library of Australia's Twitter account, it is very similar to the State Library of Victoria's Facebook account with how is strongly promotes their exhibitions and important news.
National Library of Australia