Purpose – As organisations are increasing their investment in social media marketing (SMM), evaluation of such techniques is becoming increasingly important. The purpose of this paper is to contribute to knowledge regarding SMM strategy by developing a stage model of SMM evaluation and uncovering the challenges in this process. Design/methodology/approach – Interviews were conducted with 18 key informants working for specialist SMM agencies. Such informants are a particularly rich source, since they manage social media campaigns for a wide range of clients. An exploratory research was conducted and thematic analysis surfaced the key components of the SMM evaluation process and associated challenges. Findings – The SMM evaluation framework is developed. This framework has the following six stages: setting evaluation objectives, identifying key performance indicators (KPIs), identifying metrics, data collection and analysis, report generation and management decision making. Challenges associated with each stage of the framework are identified, and discussed with a view to better understanding decision making associated with social media strategies. Two key challenges are the agency-client relationship and the available social analytics tools. Originality/value – Despite an increasing body of research on social media objectives, KPIs and metrics, no previous study has explored how these components are embedded in a marketing campaign planning process. The paper also offers insights in the factors that make SMM evaluation complex and challenging. Recommendations for further research and practice are offered.