Collaborative communities are learning communities aimed at accomplishing common goals within often complex collaboration ecosystems. Their development requires catalyzing the process of co-discovering collaborative common ground. BoostINNO was an EU networking project aimed at building a collaborative community in which ten major European cities who are leaders in social innovation shared knowledge lessons learnt. We show how the CommunitySensor participatory community network mapping methodology and the Kumu online network visualization tool were combined to support participatory collaboration mapping among the BoostINNO community members. Two experiments were conducted: (1) finding collaboration partners and (2) comparing social innovation lessons learnt on urban spaces developed by each of the cities. We found that the mapping process indeed helped to trigger and focus productive sensemaking conversations. Limitations include the complexities of the maps, the mapping technology, and lack of dedicated time for sensemaking processes. Still, promising proof of concept has been shown in using participatory collaboration mapping for common agenda setting towards collective impact.