SAN FRANCISCO -- Police have had no luck in finding a 5-month-old girl who went missing Sunday evening, and with each passing hour the search is becoming more difficult, San Francisco police Officer Maria Oropeza said.

Someone snatched the girl from a car parked on the bustling intersection of 18th and Mission streets around 7:30 p.m., according to police.

The girl's father told police he left the infant in the car because he was going into a store. He returned shortly afterward and began driving away, only noticing the baby was gone seconds later, according to police.

The father then ran back into the store and called 911.

Police will not consider charging the father, who they said has a dating relationship with the baby's mother, with neglect or endangerment until the child is found, Oropeza said.

Investigators are working with the infant's family to determine if anyone would have planned to abduct the child.

"Right now we don't know if it's a random kidnapping," Oropeza said. Several officers have been committed to finding the infant, but police are also relying on the public's help. Anyone who saw the abduction take place is urged to call the Police Department's anonymous tip line at (415) 575-4444.