In recent years, studies about trend detection in online social media streams have begun to emerge. Since not all users are likely to always be interested in the same set of trends, some of the research also focused on personalizing the trends by using some predefined personalized context. In this paper, we take this problem further to a setting in which the user's context is not predefined, but rather determined as the user issues a query. This presents a new challenge since trends cannot be computed ahead of time using high latency algorithms. We present RT-Trend, an online trend detection algorithm that promptly finds relevant in-context trends as users issue search queries over a dataset of documents. We evaluate our approach using real data from an online social network by assessing its ability to predict actual activity increase of social network entities in the context of a search result. Since we implemented this feature into an existing tool with an active pool of users, we also report click data, which suggests positive feedback.