Trippenbach joins the Paris-based group after a stint working on a freelance basis through his own company, Trippenbach.com, which was formed after he left the BBC in Summer 2009. Later that year, he was commissioned by the broadcaster to head its groundbreaking nationwide interactive class survey.
Trippenbach told Journalism.co.uk today that Citizenside was "an excellent concept, something I really believe in".
"Anyone can have the ability to film and edit really good quality footage from their pockets. It simply makes sense to use that."
Trippenbach acknowledged that other groups were making use of user-generated content (UGC), including the BBC's UGC hub, but said there were "a lot of problems" with the traditional newsroom way of engaging with users. He cited the "real sense of community" at Citizenside as a reason for joining the team.
As well as overseeing the editorial operation, Trippenbach will be working to "further the social gaming element" of the network, "using the dynamics of gaming to get people engaged", he said.
Citizenside has already formed partnerships with a number of French media outlets including 20 Minutes, Metro International, Le Parisien, Agence France Presse and Voici, which use Citizenside's Reporter Kit to collect images from users.
The agency has plans to expand internationally, Trippenbach said, and will be focusing on its English-language site. His new role will see him divide his time between Paris and London.
Director and co-founder of the Citizenside Philippe Checinski said: "Philip's editorial credentials are rock-solid, with a long history as a journalist at the BBC and the CBC.
"His editorial judgement and innovating instincts together make a powerful combination, and we’re proud to have him on board."
Fellow co-founder Matthieu Stefani left the group in January following the recent launch of a new version of the site. Stefani started Citizenside with Checinski and Julien Robert in 2006, raising funds through investments by the Agence France-Presse (AFP) and IAM in 2007.