Wife Asks Ahmadinejad for Help Finding Missing Ex-FBI Agent Husband As Mahmoud Ahmadinejad prepares to speak to the United Nations General Assembly in New York on Wednesday, an electronic billboard in Times Square and subway placards around the city will remind the Iranian president and U.N. delegates of an American who has been missing in Iran for more than five years. "I'm trying to make the public realize that my husband is the second-longest held hostage in American history," said Christine Levinson, husband of former FBI agent Robert Levinson. It's been five and a half years since he disappeared on Kish Island and two years since we received a video from his captors . . . and we still have no information about Bob since the day he disappeared. "This week, with the UN General Assembly in New York," Christine Levinson told ABC News, "we are trying to get the whole world's attention. I am hoping we will finally be able to get him home. Robert Levinson, a father of seven and grandfather of two, began working as a private detective after leaving the FBI. He disappeared in March 9, 2007 while on a business trip to the Iranian resort island of Kish. U.S. officials believe he is being held by unknown captors in Southwest Asia. Five months after his disappearance, against the advice of the U.S. government, Christine Levinson and her son traveled to Tehran to conduct their own investigation, but the trip yielded no results. The Levinson family received a so-called "proof of life" video in late 2010 showing Levinson, who suffers from diabetes and high blood pressure, in deteriorating health. Levinson, who was 62 at the time, addressed Christine as "my beautiful, my loving, my loyal wife" and referred to his 33 years of service to the federal government before pleading for help from U.S. authorities. Christine Levinson is now appealing directly to Ahmadinejad, who is under the international spotlight as he prefers to give his final speech to the U.N. as Iranian president. He leaves office next year. "In the past he has said that he will investigate and he will have his people investigate," Levinson told CNN. He has promised to help us. So we need to get him in touch with whoever can help us get the job done and get Bob home. Pictures of Levinson began appearing on subway placards in Midtown Manhattan last week. The signs, and a Times Square billboard, feature a picture of Levinson next to the word "Missing" and ask United Nations delegates to "encourage the Islamic Republic of Iran to work with the U.S. to bring Bob home." This year the FBI offered a $1 million reward for information. The case has frustrated investigators, whose diplomatic strategies have failed. "We ask ourselves how is it possible that someone -- especially someone 6'4? and (then) 225 pounds -- disappears without a trace," reads a statement from the Levinsons on the family's website. Iranian representatives did not respond immediately to a request for comment.