Other Twitter users began sharing a link to Race2Recover.com, which is encouraging runners to donate their hotel rooms to displaced residents.
But some runners, especially those who traveled from outside the United States to participate in the race, were frustrated by the last-minute cancellation of an event in which not everyone is guaranteed a bib.
To guarantee a spot in the race, runners must pledge to do the event for charity or qualify with a fast marathon or half-marathon time. For the majority of the race participants, they're in by being one of the lucky ones chosen in a random drawing.
"It's a huge frustration," said Juan Carlos Arevalo, who traveled from Argentina. "It really is an effort to come here and participate."
Neil Robbins flew in from Scotland on Thursday, planning to run the race to raise money for cancer research. Now he'll be spending the next week in New York.
"I tried my best. I did my training. I came across, but unfortunately ... Sandy has put an end to my dream," he said. "But such is life. I'll try again next year, maybe."
Wednesday, in announcing his decision to move forward with the race, Bloomberg said "an awful lot of small businesses" depend on the annual event.
On Thursday, the mayor brushed aside concerns that the marathon would direct crucial resources away from recovery efforts, saying electricity would be restored by race day, thus freeing up police currently manning intersections where the traffic signals and electricity have gone out.
"To host the New York City Marathon in the middle of what is complete devastation and a crisis in parts of this city is just wrong," said City Councilman Domenic Recchia, whose south Brooklyn district includes Coney Island and other areas that suffered heavy damage.
Bloomberg continued his fight for the marathon early Friday, recalling another time when city officials were forced to make a tough decision during a sensitive time.
"As Rudy Giuliani said to me this morning, he said, 'You know, right after 9/11 people said exactly the same thing.'" Bloomberg said, adding, "You have to keep going and doing things and you can grieve, you can cry and you can laugh all at the same time. That's what human beings are good at."
City and race officials met throughout the week, up until Friday afternoon, weighing their options including considering whether to postpone the race or shorten the course.
In the end though, "it was clear that this was not going to be a celebration of New York," said Deputy Mayor Howard Wolfson. "It was going to be a divisive, difficult day instead of a day of celebration."
Shortly after 5 p.m., the cancellation announcement was made.
Mike Denton, a New Yorker who was set to run the race, said he was looking forward to the opportunity to "use this as a way to build some energy and kind of remind myself why New York is awesome."
Now, he said, five months of training is "for nothing."
Others expressed concern for the economic implications of canceling such a huge revenue-generating event.
Olympic marathoner and former New York City Marathon champion Paula Radcliffe said on Twitter that the city needs "the solidarity, the lift, and the economic boost that Marathon Sunday brings to NYC."
Tony Ruiz, a running coach with the Central Park Track Club, said Thursday that the consequences of canceling "would be very severe and possibly hurt the city even more, and certainly hurt economically."
The marathon is also an important fund-raiser for hundreds of charities who recruit runners to raise funds, and they stand to lose their pledged donations, said Lee Silverman, president of JackRabbit Sports, a running gear retailer that works with many of those charities every year. More than $34 million was raised in 2011 by runners doing the race for charity, according to the marathon website.