President Barack Obama and his administration have repeatedly pressed Iranians to provide information on former FBI agent Robert Levinson, an American who went missing in Iran eight years ago, White House spokesman Josh Earnest said on Tuesday.The White House believes Levinson is no longer in Iran, Earnest said at a news briefing, but will continue to press the Iranians for "as much information as they have about his whereabouts."Earnest said the White House have been in touch with the Levinson family as recently as December. "We're obviously very sensitive to the concerns of the Levinson family," Earnest said.Asked if the US government knew if Levinson was alive, he said he did not have an updated assessment. Levinson's family said on Tuesday it was "desperate for answers" on his whereabouts and expressed frustration at the information it had received from the Obama administration.Levinson, who disappeared while visiting Iran's Kish Island in 2007, was not among the five American prisoners released by the Iranian government on Saturday as part of a prisoner swap with Washington.His family said in a statement over the weekend that they were "devastated," adding: "We are happy for the other families. But once again, Bob Levinson has been left behind."In a speech on Sunday celebrating the release of the Americans, Obama said the US government would "not rest" until Levinson was found. US Secretary of State John Kerry said in a Twitter post that Iran had agreed to deeper coordination to locate Levinson.Levinson's son, Dan, told CNN on Tuesday the family "can only hope that they (US officials) are really doing everything they can."He said that for years "President Obama has promised that, Secretary Kerry has promised that, but it hasn't ... given us results."US officials believe that Levinson, who suffered from diabetes, died in captivity after meeting with an American-born Islamic militant on Kish Island. Iranian officials have repeatedly denied knowledge of his disappearance or whereabouts.Robert Levinson's wife, Christine, told CNN on Tuesday that she had tried since November to arrange face-to-face meetings with high-level administration officials, including Obama, Kerry and national security advisor Susan Rice."We're desperate for answers, and we're really going to push hard, and we're not going to go away," Christine Levinson said.She said the family had received one phone call from a member of the Obama administration after the American prisoners' release apologizing that they had not been warned ahead of time.In a separate interview on Fox News, Christine Levinson said, "we need the United States government to work harder to bring him home." US Deputy Secretary of State Antony Blinken said on CNN that officials have been working to find Levinson and bring him back "the entire time." He said the administration was uncertain Levinson was still being held in Iran.The FBI has offered a reward of $5 million for information leading to finding Levinson and his return.