Rodman called on Kim to "do me a solid" and release Kenneth Bae, who was sentenced to 15 years of hard labor after being convicted in April of "hostile acts" against North Korea, CNN reported Wednesday.
"I'm calling on the Supreme Leader of North Korea or as I call him "Kim", to do me a solid and cut Kenneth Bae loose," Rodman tweeted.
Bae, a Korean-American, was arrested Nov. 3 in Rason City as a tourist. His sister, Terri Chung, told CNN last week her brother isn't a spy but a tour company owner who was in North Korea for work.
U.S. officials have been trying to learn what Bae did wrong because the North Korean statement about his conviction had no details of the allegations against him.
"This was somebody who was a tour operator, who has been there in the past and has a visa to go to the North," a senior U.S. official told CNN Monday.
NK News, a U.S. website that deals with North Korea, suggests Bae was a missionary who was trying to convert North Koreans, CNN said.
Rodman, an NBA Hall of Famer, captured headlines when he befriended Kim during a visit to Pyongyang in February. He stressed he wasn't an official diplomat between the United States and North Korea.
"I'm not a politician," Rodman tweeted. "Kim Jung Un & North Korean people are basketball fans. I love everyone. Period. End of story."