Sun was last seen at her home on Blackhawk Drive in Sacramento, California on September 7, 2007. She and her husband, Dennis Yen, were in the process of a divorce at the time. He says he last saw her when she left the residence to meet her boyfriend and collect some money the boyfriend owed her. Sun has never been heard from again. A few days after she was last seen, Yen found her car in the parking lot of the former Florin Mall. There was no sign of Sun at the scene. Her husband reported her missing on September 12.

Yen stated several weeks after Sun's disappearance, a woman went to his home and gave him Sun's driver's license and a photo of her young son which she normally carried with her. The woman claimed the items were mailed to her by the post office after being found loose inside a mailbox.

Sun is considered to be at risk because it is uncharacteristic of her to leave without warning. Her disappearance remains unsolved.