Cops are searching for a 7-year-old boy who vanished from his Brooklyn foster home after living there for less than three weeks.

Patrick Alford, 7, had been taken from his biological parents just days ago and was homesick, his foster family said.

At 9 p.m. Friday, he accompanied his foster mother to the trash compactor at their East New York home. When his mom turned her back, Patrick, 4-foot-8 and 65 pounds, slipped away.

“My mother is hysterical right now,” said the foster mom’s daughter, who asked not to be identified by name. “It’s very tragic, but so far no news.”

The daughter said her mother has been taking in foster children for more than 20 years without incident.

Patrick’s sister, “J.J.”, 4, who is also being cared for by the foster family, “wishes he would come back,” she said.

The boy was last seen wearing a red T-shirt, blue jeans and black sneakers, police said.