At a time when Web 2.0 applications in libraries have gained growing popularity globally, it appears that the library must consider marketing its services more regularly through the Internet, taking advantage of Web 2.0 applications to improve access to its users and to promote information services. Many studies have discussed the importance of enhancing library services through Web 2.0 applications such as blogs, wikis, RSS (Really Simple Syndication), podcasts and social networking sites (SNSs). However, very few studies have focused on social networking sites in relation to marketing strategies for library and information services. The main purpose of this paper is to explore the varied marketing activities of libraries on SNSs, focusing on Facebook, as it is recognized as a popular SNS used among libraries. Additionally, the study introduces the role of library and information professionals (LIPs) within SNSs, as well as user contributions to the marketing process. Web content is used in a quantitative approach. Twenty public libraries that have Facebook pages have been selected as subject samples.