Dennen co-founded the mobile blogging platform Moblog, formerly MoblogUK, in November 2003. Commercial users of the service have included Ronan Keating, Bloc Party, Greenpeace, Elbow, Imogen Heap, Max Clifford, Channel 4, Oxfam, Amnesty International and Comic Relief. The service gained prominence in 2005 when Eliot Ward uploaded to the site from one of the London Underground bombings.