The search for mute, autistic New York City teenager Avonte Oquendo has expanded to New Jersey and Long Island as the reward for his safe return rose to $77,500.

Avonte, 14, who is nonverbal, has been missing since Oct. 4, when he walked out of the Center Boulevard School in the Long Island City section of Queens. Avonte requires constant supervision at school, and it’s unclear why an aide wasn’t with him or security didn’t stop him from leaving the school.

Avonte’s fascination with trains led police to search train yards and subway tunnels in hopes of finding the mute, autistic teen. Now New York City Police Commissioner Ray Kelly said authorities are investigating the possibility that Avonte may have ridden a train out of the city, CBS New York reported Tuesday.

Meanwhile, the reward for Avonte's safe return has risen to $77,500, CNN reported.

"We have redoubled our efforts. We have hundreds of police officers and detectives engaged in this search. We've enlisted the help of the Guardian Angels Society, many volunteers,” Kelly said during Monday’s Columbus Day Parade in Manhattan.

Posters of Avonte have been posted all over New York City streets and subway stations as the mute, autistic teen’s family hopes he will be found alive.

"We're just out here trying to give out as much information as we can to anyone that wants to help or volunteer or search for Avonte," his Daniel Oquendo Jr. told ABC New York. "We're trying to have a family member or relative out here 24 hours a day, just in case he comes back here or anybody else wanders up here and wants to help."

Avonte’s grandmother, Doris McCoy, also had a message to anyone who may have taken her grandson.

"Please bring him back, don't keep him if you have him," McCoy said, adding that she believes someone has her grandson and that he is alive. "Be good to him. Don't abuse him. Don't hurt him."

The family’s optimism stems in part because Avonte has wandered off before and he returned safely home.

Anyone with information on Avonte’s whereabouts was urged to call Crime Stoppers at 1-800-577-TIPS. Tips can also be submitted via text to 274637 (CRIMES) and entering TIP577.