Aurelio Teran, 38, allegedly committed the crime about 6:15 a.m. at the residence in the 4900 block of Woodman Avenue. The child then ran out of the unit and yelled for help, according to Los Angeles Police Department investigators.
"Once the neighbors made entry into the bedroom, the suspect was gone," said Capt. Lillian Carranza, an LAPD spokeswoman, adding that the boy was uninjured.
Officers responded to a report of an assault with a deadly weapon and found the 31-year-old victim suffering from stab wounds to her body, said LAPD Officer Norma Eisenman.
Viridiana Teran was transported to UCLA Medical Center, where she later died.
Aurelio Teran is believed to be driving his work vehicle, a gray 2006 Ford F-150 pickup truck with stenciled advertising on its side for "Viry's House Cleaning." The truck's California license plate number is 8E94842.
The weapon was recovered, investigators said, adding that the suspect should be considered armed and dangerous.
"Anybody that would have the gall to kill their wife of 12 years in the presence of their son - really, that's very telling," said LAPD Lt. Michael Kocak.
The motive for the killing was unknown. Police said the attack happened about 15 minutes after Aurelio Teran returned home from work.
The boy was placed in protective custody after the incident.
"He only had his mom, and now his dad is considered a fugitive," Carranza said.
As part of the search for the suspect, police have notified the U.S. Customs and Border Protection, the FBI and the California Highway Patrol.
Anyone with information about Teran's whereabouts is asked to call 911 or LAPD Van Nuys Division detectives at (818) 374-9500.