Nic Wilkins started selling parts of his sneaker collection online two years ago as a way to make some extra cash in college. The hobby took off, and this year he expects to move 10,000 pairs of shoes. His anticipated take is a 25 percent profit from over $1 million in sales.

The main website enabling Mr. Wilkins’s now full-time business? StockX, a site that treats coveted consumer goods like sneakers as tradable commodities.

Sneaker collecting and trading “just keeps growing,” said Mr. Wilkins, a 24-year-old San Francisco resident who recently hired a business partner to manage his shoe inventory at a warehouse in upstate New York. “It is absolutely wild.”

StockX is part of a burgeoning group of online marketplaces that have turned resales of sneakers into a kind of currency — and an increasingly big business. Other sites like GOAT Group, Stadium Goods and Bump, which also resell sneakers, streetwear and other goods, have raised more than $200 million in venture capital funding. On Wednesday, StockX said it had hired a new chief executive to expand its business and garnered a fresh $110 million in financing that values it at more than $1 billion.