WASHINGTON (Reuters) - The family of a former FBI agent who vanished in Iran in 2007 has released a hostage video showing him alive and asking for help. The video shows Robert Levinson, looking gaunt, asking for the US government's help "to answer the requests of the group that has held me for 3-1/2 years". He does not identify the group in the footage, posted on a website dedicated to his release. Levinson's son and wife on Friday also posted a video message on the website, asking his captors to tell them their demands for his release.