Barnes took to his Twitter and Instagram accounts Tuesday, asking anyone who knows the whereabouts of 51-year-old Michael Williams of Sacramento to call police.
Barnes also posted photos of Williams on his accounts. Williams is married to Barnes' aunt, 48-year-old Tanganyika Williams.
Sacramento police say Michael Williams is suspected of fatally stabbing his wife. Her body was found lying on a street July 8.
Officer Michele Gigante, a police spokeswoman, says an arrest warrant is out for Williams, who apparently was last seen in south Sacramento on Monday.
Gigante says police appreciate that Barnes is using his status to help find the suspect.