Neeson and sons - Micheal, 13, and Daniel, 12 - attended the Upper East Side's American Irish Historical Society, as well as Richardson's mother, Vanessa Redgrave, and sister, Joely Richardson.
Also attending were Mike Nichols, Diane Sawyer, Matthew Modine, Ralph Fiennes, Uma Thurman and Mathilde Krim of the American Foundation of AIDS Research - amfAR, the charity for which Richardson had served on its board of trustees since 2006.
"She looked incredibly beautiful," Krim said, adding that everyone appeared to in a state of shock and Neeson appeared distraught as he received everybody.
Earlier Friday, friends continued to expressed their shock and grief over her death from the fall she took on a ski slope.
"Natasha was a very close friend of our family, so it's been a very, very sad few days and I think it will stay that way for a good while," Matthew Broderick said. "It's hard to say."
Actor Jonathan Cake said: "I had dinner with her Saturday night. Just the two of us. Saturday night, last Saturday. She left to ski the next day."
The private viewing followed Thursday night's tribute when Broadway theaters dimmed their lights to mark her death.
Richardson, 45, died Wednesday at Lenox Hill Hospital after falling at the Mont Tremblant resort in Quebec on Monday. The New York City medical examiner's office ruled Thursday her death was an accident.
Meanwhile, Montreal's top head trauma doctor said Friday that the lack of medical helicopters in the province of Quebec may have played a role in Richardson's death.
"It's impossible for me to comment specifically about her case, but what I could say is ... driving to Mont Tremblant from the city (Montreal) is a 2 1/2-hour trip, and the closest trauma center is in the city. Our system isn't set up for traumas and doesn't match what's available in other Canadian cities, let alone in the States," said Tarek Razek, director of trauma services for the McGill University Health Centre, which represents six of Montreal's hospitals.
Being driven by ambulance to two separate hospitals rather than airlifted by helicopter directly to a trauma center could have cost Richardson crucial moments, he said.
"A helicopter is obviously the fastest way to get from Point A to Point B," he said.
Centre Hospitalier Laurentien, the first treatment center Richardson was brought to, does not specialize in head traumas, so her speedy transfer to Sacre Coeur Hospital in Montreal was critical, said Razek.
"It's one of the classic presentations of head injuries, `talking and dying,' where they may lose consciousness for a minute, but then feel fine," said Razek.
Razek said immediate treatment might have helped Richardson but added: "There are so many variables it's hard to speculate what might have been done differently."
Associated Press Writer Amy Lutz in Mont Trembland contributed to this report.