Allbirds has around 15 staff working at its San Francisco office as well as contractors in New Zealand.
"It's really exciting times for us at the moment," Brown said. "Sales are going really well. When we first raised that money we sat down with our seed investors and set a target for the end of this year and they kind of laughed at us and now we're on track to probably triple that."
"And we could have maybe done more, but the biggest challenge has been making them fast enough."
The shoes, which cost around $95 on the Allbirds website, are touted as being an eco-friendly and comfortable wool shoe, and have already been selling well in the US and New Zealand although Brown said they were just beginning..
"Basically we're on a mission to try and make shoes more sustainable - bottom line," Brown said.
"So we've started with a wool shoe and we think there's a range of other natural materials that have been ignored by the footwear industry," he said.
"So we're trying to do things better and make shoes that are comfortable and more sustainable, and we've only just started."