Like generations of garment workers before him, Max Hernandez came to New York City to get his start behind a sewing machine.

Only he could not find any work. After more than a year of looking, Mr. Hernandez, 25, finally spotted a Craigslist ad for a $12-an-hour sewing job with UZI, a tiny company in Sunset Park, Brooklyn, that makes dresses for Anthropologie, among others.

“New York City is the center of the fashion world, but hardly any of it is made here,” said Mr. Hernandez, who beat out a dozen other applicants for the job. After several promotions, he now makes $15.50 an hour.

As Fashion Week unfolds on glittering runways this week, the city’s once-thriving garment manufacturing industry has little to celebrate. Many companies are struggling with rising rents and labor costs and outdated work spaces and losing business to competitors overseas who can make clothes more cheaply. Block after block of factories and showrooms have disappeared from the renowned garment district in Manhattan, replaced by technology, media and consulting companies that focus on the design and marketing side of the business, if they are even connected to fashion.