Vehicles have been covered with missing posters
A help centre has been set up for those looking for someone at the Armory in Lexington Avenue.
Driven by desperation, more than 2,500 people stood in line at a centre on Thursday.
They clutched posters and photographs of their missing relatives and friends, hoping they would lead to information of their whereabouts.
They were also asked to bring in toothbrushes and other personal items belonging to the missing person that might contain a tiny bit of DNA that could be matched against a body, or part of a body.
The family and friends queuing at the centre feared the worse but were hoping for something better.
Zara Kahn held photographs of her brother, 29-year-old Taimour Kahn.
'No luck'
Her mother pressed fliers into the hands of strangers which asked people to call with information, followed by a telephone number.
"If anybody has heard anything, anything, we've been searching days," said Ms Kahn.
Alice Carpeneto got a phone message and nothing else from her daughter Joyce, who worked on the 83rd floor of one of the towers.
"She was on the machine, saying 'Mom, we've been hit by a plane and I'm leaving'" said Mrs Carpeneto.
Medical records
Her daughter's best friend and co-worker got out. That has comforted Mrs Carpeneto and given her hope, but she has called every hospital without luck.
"As every hour goes on, it just gets worse," said family friend Deborah Burton.
"But we're not giving up, because we know that means the end."
At New York's St Vincent's Hospital, where many of the victims from the attack were taken, relatives also waited to find out if their loved ones had been admitted.
Nearby vehicles were plastered with missing posters.
Emily Howell was looking for her husband with her son Kevin.
She said: "I came to the hospital with information. Hopefully when they do bring out and recover more people, if by any chance he comes out alive at least I have the medical record the hospitals can use.
"If he is not alive then it will still tie him to something. Without that they wouldn't know who was who."
Some relatives had been trying to persuade reporters at the hospital to print or broadcast the names and photographs of the relatives they could not find.