Most of existing online social networks, such as Facebook and Twitter, are designed to bias towards information disclosure to a large audience. Google recently launched a new social network platform, Google+. By introducing the notion of `circles', Google+ enables users to selectively share data with specific groups within their personal network, rather than sharing with all of their social connections at once. Although Google+ can help mitigate the gap between the individuals' expectations and their actual privacy settings, it still only allows a single user to restrict access to her/his data but cannot provide any mechanism to enforce privacy concerns over data associated with multiple users. In this paper, we propose an approach to facilitate collaborative privacy management of shared data in Google+. We extend and formulate a multiparty access control model, named MPAC+, to capture the essence of collaborative authorization requirements in Google+, along with a multiparty policy specification scheme and a policy enforcement mechanism. We also discuss a proof-of-concept prototype of our approach and describe system evaluation and usability study of our prototype.