Jennifer Hudson, the singer and Oscar-winning actress, appealed to the public yesterday to help find her seven-year-old nephew who has been missing since her mother and brother were shot dead in Chicago on Friday.

The star flew to Chicago after the bodies of her mother, Darnell Donerson, 57, and brother Jason Hudson, 29, were discovered on Friday in Ms Donerson's home. Police sources said Hudson had assisted in identifying them.

Last night, mystery still surrounded the whereabouts of Hudson's nephew, Julian King, who may have witnessed the killings. A city-wide search was underway and appeared to be focused in the neighbourhoods close to the murder scene. Flyers were being distributed to help find the child.

The tragedy struck as Hudson prepared to start a worldwide tour today to promote her new, self-titled album. She will now remain in Chicago.

Hudson, 27, began her rise to fame on American Idol. Her Oscar-winning performance in the 2007 film Dreamgirls catapulted her to stardom. She had a significant role in the film Sex and the City and stars alongside Queen Latifah in The Secret Life of Bees.

Hudson was close to her mother and had urged her to move to a safer area of Chicago, away from the South Side where she had lived for years.

She has appealed for information about her nephew on her MySpace blog: "Thank you all for your prayers and your calls. Please keep praying for our family and that we get Julian King back home safely. If anyone has any information about his whereabouts please contact the authorities."

William Balfour, the estranged husband of Hudson's sister, Julia, was still in custody last night. He has been on parole after serving seven years in prison for attempted murder. Chicago police said he remained only a "person of interest" to the investigation and had not been charged with any crimes, nor was he being treated as a suspect.

Autopsy results released on Saturday confirmed that both victims had died from gunshot wounds. Police said they had found no motive, and no weapon in a search of the house.

"From what we know right now, it appears to be some type of domestic situation, but that's very preliminary," said the Chicago Police Department superintendent Jody Weis.

Mr Balfour's mother insisted her son was innocent. "This is not my son that did this. You cannot say my child did this to that girl. He loved Julia. He loved Julia's mother. My God, he put that girl's mother before me," Michele Davis Balfour said. On Saturday, Julia Hudson made her own plea for her son's safe return. "All I ask, I don't care who you are, just let the baby go. Please," she said at the Pleasant Gift Missionary Baptist Church. "My biggest fear has already happened. My greatest hope is finding my child."