NEW YORK — Some 300 eager collectors descended on a drab hotel conference room in Midtown Manhattan last month for the annual international show hosted by the Metropolitan Postcard Club of New York City. Over two days, as they rummaged through the roughly 800,000 cards of the 30 dealers, most were hunting for obscure, beautiful or intriguing postcards to add to their collections. But an impassioned subset was after something far more resonant and elusive. They were searching for lost New York.

This quest meant different things to each of them, for every longtime lover of Gotham has his own, personal version of the vanished city.

For Dan O’Neill, a retired history teacher, the streetscape he sought to revisit was that of his 1950s childhood in Bayside, Queens. (“I marched in the Little League parade for eight years,” he said, “and if I come across a card of Bell Boulevard, I’ve hit the jackpot.”)

For Dan Pisark, head of retail services for the 34th Street Partnership, a business improvement district that includes Macy’s, the destination was any long-defunct shopping emporium. (“My mother was a dedicated department store shopper, and she used to take me on the Sea Beach line to A. & S.” and Martin’s in Downtown Brooklyn, he said. “I have in my collection a photo of where I sat with Santa in 1958.”)

And for Miriam Berman, a graphic designer who once worked in the 1902 Flatiron Building, the neighborhood she longed to stroll was the glamorous Madison Square of the early 20th century.

Members of the Metropolitan club generally meet monthly to swap gossip and vintage postcards, often keeping an eye out between gatherings for unusual items that will enrich one another’s highly individualized collections. It was Pisark who gave Berman her most prized artifact of old New York — as precious to her as a signed Babe Ruth card would be to a baseball card collector.

In 1912, America’s first public Christmas tree — a 63-foot balsam fir — was ceremoniously displayed in Madison Square, initiating an annual ritual imitated thereafter across the country. Yet in years of research, Berman had never found a single photographic print depicting that inaugural fir.

Then a few months ago, Pisark, knowing only that she was a Madison Square aficionado, sent her a scan of a random card that just happened to contain all necessary documentary evidence to prove that it portrayed that granddaddy of all public holiday trees. Postmarked in January 1913, it was a “real photo postcard” — a photograph taken by an individual and turned into a one-of-a-kind postcard by a film processor — that showed the giant fir with the majestic Stanford White-designed Madison Square Garden behind it. On the card a man had written to his mother: “I took this picture Xmas day,” adding on the front, “Christmas tree for everybody, Madison Square… 1912.”

“He didn’t know that tree was one of my passions,” Berman said of Pisark. “But I’m gasping for air when I open the email and I’m looking at the picture of that card.”

Berman said that before a friend took her to her first postcard show in the 1980s, she knew nothing about the history of the Flatiron Building or its environs. But her journey down the rabbit hole of postcard collecting opened her up to various vibrant, earlier incarnations of the area. In making the past present, her ever-growing hoard of cards taught her that she lives in a palimpsest of a city, layers of past streetscapes poking out from beneath the current ones.

Ambling along Madison Square West through the antique postcards and photographs she found, Berman passed the white-marble 1859 Fifth Avenue Hotel (a spot occupied today by the Fifth Avenue Building, home to Eataly) and stumbled upon Delmonico’s, the famously elegant restaurant built at 26th Street in 1876. Next door, she observed a four-story townhouse.

Venturing across 26th and looking back at the same corner via a later postcard, Berman discovered that the Delmonico’s building had been topped off with a new mansard roof and remodeled as Café Martin. And the adjoining brownstone was now gone, replaced by the 1905 Beaux-Arts-style Cross Chambers Building, luxury bachelor apartments stacked above a swanky store for Mark Cross, the leather-goods maker. (In 1984, Berman would move her office to the Cross Chambers.)

Card by card, year by year, Berman reconstructed the entire periphery of the park, ultimately turning her passion into a lushly illustrated book, “Madison Square: The Park and Its Celebrated Landmarks.”

“It’s like putting together a great puzzle,” she said.

But there are 8 million puzzles in the naked city, each collector assembling a unique one.

Among the postcard dealers at the Watson Hotel on West 57th Street was Hy Mariampolski, whose 12,000-card collection of old New York images offers a deeply personal exploration of the Lower East Side, where he grew up in the 1950s.

“Memory is an amorphous thing,” he said. “Postcards give body to memory.”

Some of his most abiding recollections are of the gracious, red brick and brownstone building at 425 Lafayette Street. Most New Yorkers know the structure as the Joseph Papp Public Theater. Some are aware that it was originally the Astor Library (of which Mariampolski has a black-and-white 1905 postcard).

But for Mariampolski, who was born to Polish Jewish survivors of Auschwitz in a refugee camp in Germany in 1947, the building was his first home in America. For decades before Papp transformed the library into a theater complex starting in 1967, 425 Lafayette housed the Hebrew Immigrant Aid Society, which sheltered Mariampolski and his parents when they immigrated in 1950.

“There’s a theater there where I can literally point to the corner and say, ‘This is the first place I slept in America,’” he said. “In one way it’s wonderful, and in another it’s a shock of realization.”

Mariampolski acquired his first postcard at age 11, and as a globe-trotting market researcher in subsequent decades, he said, he haunted “flea markets and antique dungeons” from Budapest to Buenos Aires, buying up period postcards of New York mailed home by tourists.

“I was trying to recover my biography, trying to recover the streets,” he said. “It became an obsession.”

His collection is particularly strong in cards depicting the Yiddish theater district on lower Second Avenue, where his parents sometimes took him in the 1950s. And he especially loves cards showing immigrants “earning their livelihood right on the street,” images that evoke the pushcarts he visited with his father on Avenue C.

“I used to like erotic cards,” he recalled, covering his mouth with his hand and adding in a stage whisper, “Once, my dad bought a few.”

In living his life with one foot in New York’s past, Mariampolski was right at home at the postcard show. In a back corner, Pisark, the department-store aficionado, was shooting the breeze with Bob Stonehill, a Queens native who has amassed 30,000 New York postcards, an archive-quality collection for which he built an addition on his house.

“Those were the biggies,” Stonehill said when his friend mentioned Macy’s and A & S, “but I just saw a card of H.B. Claflin,” a long-gone dry-goods wholesaler with a colossal 1861 Italianate building on Worth Street.

And when it came time to bid farewell until the next gathering of New York postcard obsessives, Pisark alluded to another vanished city landmark. Turning to go, he gave a small smile and said, “See you at Gimbels.”

This article originally appeared in The New York Times .