This article analyses conceptual metaphors produced in argumentative writing by learners of English as a second language (L2). Founded on the Conceptual Metaphor Theory, it explores the linguistic metaphorical expressions which reflect an underlying conceptual metaphor. By drawing on Critical Metaphor Analysis, this research adopts a qualitative approach to analysing the concealed motivations behind a conceptual metaphor use. The data of this study comprise five argumentative essay samples collected from foundation year students at a private university in Malaysia. This study reveals how a conceptual metaphor is evoked to frame an argument in a way that is advantageous to the participants, particularly in establishing their stance on the proposition that social media is advantageous rather than disadvantageous to its users. Seven conceptual metaphors identified from the five samples of writing are related to social media, namely global mass gathering, loudspeaker, free society, accommodation, teacher, strong force and maze. While the first six metaphors serve as rhetorical tools to aid the participants in establishing arguments, the last metaphor is raised in the counterclaim section to illustrate how the opposition could equally rely on conceptual metaphors to establish its viewpoint. In instances where the metaphors are deployed as rhetorical devices, the participants’ covert intention to convince readers of their standpoint is achieved by utilising the conceptual metaphors to illuminate abstract ideas, arouse positive or negative emotions in readers, indicate positive or negative evaluations and evoke an ideology.