This is an exploratory study investigating the use of social networking tools in academic libraries, examining the extent of their use, library staff's perceptions of their usefulness and challenges, and factors influencing decisions to use or not to use such tools. Invitations to participate in a web-based survey were sent to 140 university libraries from Asia, North America and Europe. Responses were received from 38 libraries (response rate: 27.1%). Twenty-seven libraries (71.1%) used social networking tools, five (13.1%) were potential users and six (15.8%) did not plan to use them at all. Facebook and Twitter were the most commonly adopted tools in university libraries. Most library staff had positive perceptions on the usefulness of social networking tools, but hesitancy among library staff and limited participation of users (i.e. students) were perceived to be hindrances. This study offers insights for academic librarians to make informed decisions in applying social networking tools. (Contains 5 figures and 3 tables.)