In recent years, the utilization of Internet-based social networking tools, such as the microblog Sina Weibo (http://weibo.com/), has grown rapidly in China. According to the most recent official statistics, about 309 million people used microblogs and over 275 million people used social networking websites in 2012. Many libraries in China take this opportunity to utilize these tools for information sharing and outreach. For instance, over 500 libraries have opened microblogs on the Sina platform alone. Do these tools really help libraries fulfill their goals and achieve their purposes? Some studies on this question showed positive results; others mentioned their ineffectiveness. To follow this line of research, we conducted a case study on the microblog of the East China Normal University Library, which made its initial presence on Sina Weibo in 2011. The number of its fans and followers has increased significantly, from zero to over 4,000 in 14 months. This paper investigates the interaction between the users and the Library’s microblog, and the users’ reaction to its posts since the library’s microblog was established. An analysis of the data collected from the library’s microblog between May 2011 and June 2012 shows that the content, language, writing style, frequency of microblog posting, and even the time of posting affect the users’ attention and the microblog’s effectiveness. To enhance libraries’ communication with users and dissemination of information through social networking tools, this paper offers some experience, feasible strategies, and suggestions, for instance, how to deliver information in an appealing way, how to attract more users, from both users’ and librarians’ points of view. Hopefully libraries will try to take advantage of the popular tools in order to provide better services and reach out to their users.