This study aims to explore how advocacy NGOs leverage outgroup representation and take appropriate action cues to mobilize civic engagement in a social movement. The 2×2 experimental study (N = 353) measured the impact of different outgroup representation types (abstract vs. specific) and message frames (why? frames vs. how? frames) upon group solidarity and readiness to join in collective action. The study"s findings suggest, firstly that the representation of outgroups moderate the relationship between ingroup solidarity and civic engagement, with this effect increased when respondents are exposed to a specific outgroup representation than when exposed to an abstract one; and secondly that under the suggestion of an abstract outgroup, respondents are more responsive to how? messages, while under the suggestion of a specific outgroup, they are more receptive to why? messages. The current study helps us to rethink the role of outgroup representations and message frames, which can help to bridge group boundaries and trigger a pool of individuals to take their action.