NORTH CONWAY, N.H. – Investigators say the last call made on a missing New Hampshire girl’s cellphone was at 6:30 p.m. Wednesday, about four hours after she was last seen.

Fifteen-year-old Abigail Hernandez of North Conway was last seen leaving Kennett High School on Wednesday afternoon. Police say she made it home but was gone when her mother arrived later.

WMUR-TV reports that police said Sunday they have not located the girl’s phone, but have determined that the last call was made at 6:30 p.m. It’s not clear where the call was made.

Several agencies, including the FBI, have been involved in searching for the girl by land, water and air.

The mother of Hernandez made an emotional plea for her return Saturday, four days after the girl vanished.

“Abby,” Zenya Hernandez said, her voice breaking, “I want to say please come home. We miss you so badly. We want you back with us.”

Zenya Hernandez asked Abigail’s friends to come forward with any information that could help return her safely, including whether there were recent changes in her behavior. She was mindful of the importance of the day: Abigail’s 15th birthday.

“We love you and we miss you and happy birthday, Abby,” she said.

On Monday evening, Abigail’s sister Sarah Hernandez said Abigail’s family needs to know she’s safe. She says if anyone knows where Abigail is to “keep her safe and let her” return to her family.

Assistant Attorney General Jane Young said anyone with information about Abigail should contact police. “No detail is too small,” Young said.

Police are asking the public to remain vigilant. They’ve handed out posters with photos of the missing girl and have been stopping traffic to spread the word. Billboards carry Abigail’s image and the number to call to report tips: 1-800-CALL-FBI.