Identifying terrorism-related key actors in social media is of vital signi cance for law enforcement agencies and social media organizations in their e ort to counter terrorism-related online activities. This work proposes a novel framework for the identi cation of key actors in multidimensional social networks formed by considering several dfferent types of user relationships/interactions in social media. The framework is based on a mechanism which maps the multidimensional network to a single-layer network, where several centrality measures can then be employed for detecting the key actors. The effectiveness of the proposed framework for each centrality measure is evaluated by using well-established precision-oriented evaluation metrics against a ground truth dataset, and the experimental results indicate the promising performance of our key actor identi cation framework.