There is a long history of fandom doing charitable works—almost every fan convention has at least one charity they fundraise for. Here in Atlanta, DragonCon raises funds for The American Heart Association, runs a blood drive, and partners with at least two local charities. This is not to mention the many fan-run charitable organizations running booths, panels, and events during the convention like The Harry Potter Alliance, 501st Legion, and Browncoats. Fandom's sociality and frequent focus on charitable good works undermine Robert Putnam's assertion in Bowling Alone (2000) that the social capital of America is in decline, instead I (and others) would argue that civic and social participation have only migrated to less formal locations like the fandom space of conventions and social media.
There are hundreds if not thousands of charitable organizations run by fans associated with various fandoms and media texts like Bronies for Good, as well as charities supported by celebrities and their fans like Misha Collins (Supernatural) and Random Acts. However the most iconic moment of fandom charity as modern telethon has to be the Helping Haiti Heal online event. Haiti was devestated after the earthquake and tsunami in 2010. Fans across multiple fandoms collaborated to put togther a grassroots web-athon. The Harry Potter Alliance & Leaky Cauldron live streamed (when that was technically complicated) fundraising content including Wizard Rock bands, celebrity guest interviews, fanfic readings, and an online auction (with fan-made and corporate donations). The web-athon raised over $130,000 in part because mainstream media picked up on the events and promoted them alongside the more traditional telethons happening at the time, and in part because of the divergent fandoms and celebrites involved, everything from Harry Potter (including J.K. Rowling), Hugh Laurie from House, MD, Heroes, The Wire, and True Blood -- even Twilight had an event.