Story highlights Avonte Oquendo, 14, has been missing since he ran out of his school on October 4

Transportation officials suspend overnight weekend maintenance as search goes underground

The family says the boy, who cannot communicate verbally, is fascinated by trains

Transportation officials in New York suspended overnight track maintenance on the city's transit system this weekend as workers combed the underground network for a missing teenager with autism.

Avonte Oquendo, 14, was last seen on surveillance video running out of Center Boulevard School in Long Island City on the afternoon of October 4.

The teenager, who is unable to communicate verbally, is fascinated by trains, according to his family, and officials have shifted their search underground, a spokesman for the New York Police Department told CNN Sunday.

Searches of train stations, tracks and tunnels were also conducted late last week, according to Paul J. Fleuranges of the Metropolitan Transit Authority.

A $70,000 reward has been offered for Avonte's safe return.

Avonte Oquendo, 14, of Queens, has been missing since Friday, October 4. Surveillance video shows him running away from his Long Island City school.

David Perecman, the Oquendo family's attorney, told CNN last week that he is taking steps to investigate how Avonte was able to escape school grounds unsupervised.

"Right now, we have submitted a Freedom of Information Act request to the city and the various agencies involved, in order to obtain the information for us to know what occurred," Perecman said.

Avonte's mother says the situation is "heartbreaking."

"I just need to find my son because he needs his family; he cannot fend for himself out there," Vanessa Fontaine told CNN affiliate WABC last week.

"This is just the hardest thing to have your child disappear, and you cannot bring him home with you," she said.

According to the surveillance video provided by the police department, no supervisor or monitor stopped the 14-year-old when he ran out.

"He is supposed to have one-to-one supervision at all times," Fontaine said through tears. "He has the mental capacity of a 7- or 8-year-old."

The New York City Department of Education issued a statement saying it is working closely with the police on the investigation.

The school is not commenting.

The Oquendo family filed a "notice of claim" Wednesday, said Perecman, marking the first step of a civil lawsuit against the city of New York. He declined to give further information regarding the claim.

Police say Avonte was last seen wearing a gray-striped shirt, black jeans and black sneakers. He is 5 feet, 3 inches tall and weighs 125 pounds.

Missing posters are being handed out, and the surrounding areas are under investigation, WABC reported.

"He doesn't know that, you know, 'I can get hurt in the street, someone can grab me and take me.' He doesn't know that," Fontaine said Monday. "He doesn't know fear."

Anyone with information about Avonte is asked to contact the NYPD's Crime Stoppers Hotline at 800-577-TIPS. The public can also submit tips at Crime Stoppers website, nypdcrimestoppers.com or text to 274637(CRIMES), then enter TIP577.