Platt joins the agency after seven years at Oldham-based participatory arts charity Peshkar Productions, which uses participatory arts to work with young people from disadvantaged backgrounds.
Platt explained that she hoped to use her expertise in working with audiences through socially focused projects in her newly created role of head of engagement.
"It’s about engagement and participation and helping people feel ownership of the campaigns that are targeting them," she said.
Colab founder and former Brighton & Hove head of comms John Shewell added: "The idea of co-creating projects is still a relatively new concept in comms, but Claire has been doing it for a long time.
"When you are attempting to address some of society’s most pressing issues, involving the very people we are trying to communicate with fuels a campaign that is more fit for purpose, and it’s a direction the market is starting to move towards."