Earlier in the week, Police Commissioner Ray Kelly said officers may soon scale back the search for 14-year-old Avonte Oquendo.
The boy was last seen leaving his school in Long Island City on October 4.
The search now spreads through New York City and into Westchester County.
The reward for his safe return is nearly $90,000.
Kelly says the NYPD is still devoting a lot of resources to the search, but changes may be coming he is not found soon.
The search for Oquendo, who is autistic and non-verbal, enters its 20th day Thursday.
Kelly says adjustments to lower the number of officers involved could be made this week.
"We will have to make adjustments as far as the deployment of amount of resources we have, we will do that during the week if we are unsuccessful," Kelly said Monday.
Searchers are being reminded that Avonte may be in a place they'd never think to look, hiding out somewhere to avoid crowds and people.
For more than two weeks, Daniel Oquendo and Vanessa Fontaine have been waiting for the call that their son has been found, but so far the phone has been silent.
They are now hoping that Rev. Sharpton and his National Action Network will raise the profile of their son's case and get more volunteers involved.
Family members of Avonte joined Sharpton at his Harlem headquarters, thanking New Yorkers for their support but saying more needs to be done.
"This young boy could not have left the school and disappeared in thin air," Rev. Sharpton said. "Somebody saw something, somebody knows something."
There aren't many clues in this mystery. Surveillance video shows the severely autistic 14-year-old running from his school the day he disappeared.
"This is terrible, it's like a nightmare I can't wake up from, every day I'm waiting to see my son come home," Vanessa Fontaine said.
Avonte's father adds that they are just trying to focus on bringing people out and making them aware, so they can have a large search team.
Police say Avonte was fascinated with trains and had previously turned up at subway stations after wandering off from home, so that is where investigators are focusing their energy.
Most recently, in August after he wandered away from home, family members ran to the 67th Avenue Station in Forest Hills where they found him.
Five years ago, he took the subway from Jamaica to Kew Gardens/Union Turnpike Station. Transit police found him that time. And seven years ago, he was found at the Fresh Pond Road Station in Ridgewood after wandering from home.
"Six hundred people have signed up to volunteer, and that's truly wonderful," said the Oquendo family lawyer, David Perecman. "I thank every one of them, but based on the population of the city of New York, we're missing about 8 million."
Perecman says the school district and the NYPD are refusing to turn over files that include interviews with the principal, the school's safety officer who last saw Avonte, and others. He says the family deserves answers as to what led to the teen's disappearance.
The NYPD's Marine Harbor Unit continues to search along the East River. They are searching from above, they are walking the rail yards in Sunnyside, and Auxiliary cops are walking the streets of Long Island City.
"Please bring him back, don't keep him if you have him," said grandmother Doris McCoy, who is convinced someone has her grandson and that he is still alive. "Be good to him. Don't abuse him. Don't hurt him."
Avonte was last seen wearing a gray striped shirt, black jeans and black sneakers. Authorities say that if you do see him, call authorities first and then follow the boy, because he may run if you approach him too quickly.
Anyone with information is asked to call the Crime Stoppers hotline at 1-800-577-TIPS.