There are multiple different apps based on sneakers. There are the company apps like SNKRS from Nike and aftermarket sneaker apps like StockX, Grailed, and GOAT. SNKRS is the app where all the new Nike releases are available to buy. StockX and GOAT are aftermarket apps where you can purchase any pair of sneakers, as long as someone else is selling them. StockX and GOAT have authenticity guaranteed while Grailed does not. Users don't have to worry about fakes from SNKRS since it's directly from Nike.
This market is not going anywhere anytime soon either, there are lines that are hundreds of people deep for a new release (Source)
. eBay has also entered the scene with its new authenticity guarantee over some sneakers (Source)
. The demand is so high that eBay has struggled to keep up with it.
The main demographics for sneakers are Millennials and Gen Zers. Women also make up 40% of the market but 90% of the time they are focused on high-end products (Source)