(CNN) -- The search for Avonte Oquendo, a 14-year-old autistic boy who ran out of his school two weeks ago, focused Friday on the Sunnyside East Rail Yard, a large railroad yard for passenger cars, in Long Island City, Queens, according to a source close to the investigation.
The teenager is fascinated by trains, his family has said.
The source also gave CNN new details about the widespread search for Avonte, who was last seen on surveillance video running out of Center Boulevard School in Long Island City on the afternoon of October 4. Three hours after Avonte went missing, bloodhounds traced his scent to a marshy area near his school, but then lost the trail near the water, the source said.
One hour after that, the bloodhounds picked up Avonte's scent again, this time at a subway station nearby, the source said.
Searches of train stations, tracks and tunnels are being conducted at the start of every shift by the Metropolitan Transit Authority, New York Police Commissioner Raymond Kelly said, adding that 50 NYPD officers and a task force of detectives are working the case.
Transportation officials in New York suspended overnight track maintenance on the city's transit system last weekend as workers combed the underground network. All 468 New York City subway stations have been searched, and aviation, harbor and canine officers are mobilized and deployed periodically, the NYPD said.
The previous notion that Avonte did not like water may not be correct, according to the source, who said Avonte apparently recently attended a class trip on a Circle Line Sightseeing cruise and was fascinated by the water. The NYPD had six divers in nearby water on Thursday using sonar, the source said.
For the first time in the extensive search, police have brought in the assistance of cadaver dogs, the source said.
The clothing company Old Navy also is now working with the NYPD and a federal agency, providing them with a shirt matching the one Avonte was wearing at the time of his disappearance. The source said officials will put that shirt into their database to scan video cameras for recognition, similar to facial recognition.
The Department of Environmental Protection brought in special cameras extended on poles to search the sewer system in and around the area Avonte went missing, the source said.
NYPD is also working in conjunction with the food delivery company Fresh Direct to examine its trucks. The source said there is a truck depot nearby and Avonte possibly could have gone into a truck without a driver knowing and left the area.
New York police patrol cars and search vehicles have been playing a recording of Avonte's mother calling for him into the streets, Keith Brooks, director of operations for CityWide Disaster Service, said Thursday.
"Avonte, this is your mother. You are safe. Walk toward the lights," the message repeats.
The hope is the teen, who is unable to communicate verbally, will hear the sound of his mother's voice and approach the emergency vehicles.
The extended efforts of the NYPD have led to increased awareness among New York residents, with posters and fliers filling the streets, subway alerts and city papers all spreading the same message: Have you seen Avonte Oquendo?
"I heard the day he first went missing on the news," said Alex Toroslar, a student at John Jay College of Criminal Justice. "Since then I've seen posters at Port Authority and heard announcements there."
Another New Yorker, Rachel Gilbert, said she has seen pleas to help Avonte in newspapers and on the subway.
"I was quite surprised by the individual announcement," Gilbert said, noting that she couldn't remember ever hearing a similar announcement for a missing child.
"I think the NYPD will eventually find him," Toroslar said. "It's just a matter of time because everyone in the city is aware of it."
Retta (who wished to not be identified by her last name) agreed with Toroslar but was unsure if the same intense search technique should be used in the future.
"I wonder if it were more frequent we would become more immune to it," Retta said, suggesting that New Yorkers are aware of Avonte because the search efforts have been so publicized.
The reward for the safe return of Avonte grew this week to $77,500, as divers joined an ever growing number of police and rescue officers from several states who have been searching for him nonstop for more than a week.
Avonte's mother, Vanessa Fontaine, told CNN's "Piers Morgan Live" on Thursday that she believes her son is still alive and that someone is probably holding him.
"My message to my son is that I love him and we're going to find him. You'll come home to your family. And for anyone who has him, please be kind and to let him go," she said.
Kelly said he is not holding the school safety officer who was on duty when the teen ran out of the Queens high school responsible for the boy's disappearance.
When Avonte approached the front door of his school the day he disappeared, the safety agent told him to go back upstairs, Kelly said at a news conference on Wednesday. Surveillance video then showed Avonte turning and going down another hallway, and exiting the building from a side door, he said.
Surveillance video provided by the police department shows that no supervisor or monitor stopped the 14-year-old when he ran out.
"Even though he's 14, it shouldn't matter. No one should be, you know, allowed to run around the hallways in school. And that security guard should have questioned him," Fontaine said.
David Perecman, the Oquendo family's attorney, said it took school officials at least 45 minutes to call police after Avonte left.
"I don't understand how this happens to a special needs child unless there is something in there that failed the family," he told "Piers Morgan Live" on Thursday.
The New York City Department of Education issued a statement saying it is working closely with police. The school is not commenting.
The Oquendo family filed a "notice of claim" on October 9, said Perecman, marking the first step of a lawsuit against the city of New York. He declined to give further information about the claim.
Police said 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.
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 the Crime Stoppers website,nypdcrimestoppers.com or can text to 274637 (CRIMES), then enter TIP577.
CNN's Lorenzo Ferrigno, Laura Ly and Julia Lull contributed to this report