Co-creation has become a globally popular concept in different sectors of the society. Its promise lies in breaking down hierarchies between local government, business life, universities, citizens and other stakeholders. Instead of being a top-down or bottom-up process, co-creation involves a multi-directional approach to problem solving. In this article, we scrutinize the capacity of co-creation to transform the practices of public sector in the context of urban development. In this way, we discuss both the potential and limitations of applying co-creation to the enhancement of citizen participation in cities. While new ways of acting can create novel spaces for opportunity, they also bring new winners and losers to the fore. After all, citizens are not all the same: they fall in several categories and some of them have more resources to participate in co-creative processes than others. Thus, it is relevant to know who participate in and whose voices get heard through these processes. We claim that to realise the participatory potential of co-creation, it is crucial to scrutinize actual practices through and networks within which it takes place. Through three co-creative processes from Finland, we illustrate that the promotion of participation through co-creation necessitates acknowledging the heterogeneity of citizens and taking seriously issues of urban social justice and inclusion. In conclusion, we identify issues regarding the sustainability and accessibility of participation that must be unpacked, if co-creative processes are to be used in the context of urban development.