When I Work Inc., the St. Paul software firm whose app is an increasingly popular tool for scheduling work at small businesses and temporary jobs, just attracted $15 million in new venture capital, the company said Wednesday.

Its executives also said that they expect to double the number of people at the company to about 200 over the next 18 months and that they are looking for new office space, potentially in Minneapolis. “We’ve got it narrowed down to a handful of locations,” Chief Executive Chad Halvorson said.

The company is striving to become the digital work-calendar provider to millions of Americans who have hourly full- and part-time jobs, what Halvorson calls the “deskless workforce.” The firm has a five-star-rated iPhone app and has grown from 12 to 100 employees in a little over two years.

The new funding, known as a Series B round, is led by Drive Capital, a Columbus, Ohio-based investment firm that focuses on start-ups in the Midwest. Arthur Ventures and High Alpha, which is based in Indianapolis, also participated.

“When I Work’s traction speaks for itself,” said Nick Solaro, a partner at Drive Capital. “The team built an exemplary product that addresses all-too-common operational issues for the hourly worker and employer alike.”

When I Work’s next challenge is to improve its messaging and collaboration tools that go along with its scheduling and time-and-attendance platform. The rise of Slack and HipChat have caught Halvorson’s attention — When I Work employees use HipChat at work — and he thinks When I Work can provide that service to the fluid workforce of roughly 77 million Americans who aren’t salaried and don’t work in an office.

“Tools like Slack and HipChat are great, but they are fundamentally focused on improving collaboration between people that sit behind a desk,” Halvorson said. “We think there’s a massive opportunity to build tools that improve collaboration on core business operations that serve everyone else.”

More than 20,000 companies in 50 countries — such as Uber, Dunn Brothers, Tesla, Ben & Jerry’s, Select Medical, the Columbus Zoo and Winmark — already use When I Work’s platform. Another near-term goal, Halvorson said, is to focus on international growth, which has so far happened without much specific effort.

The company moved into new offices in St. Paul in 2014 but is running out of space, and Halvorson expects to hire another 100 people over the next 18 months. He said they will announce a new location, which will have room for expansion, in either downtown Minneapolis or downtown St. Paul by early July.

The new round of funding brings When I Work’s total raised capital to $24 million. The firm was already generating $1 million in revenue per year before it sought its first round, raising $4 million in 2014 from three investors: E.ventures, Greycroft Partners and Arthur Ventures. Arthur Ventures is also a key investor in LeadPages, another of the Twin Cities’ hottest start-ups. E.ventures was one of the investors in Angie’s List, which went public in 2011.

When I Work raised another $5 million from the same three investors in 2015 and acquired a smaller competitor in Toronto, called ShiftHub.

The firm was founded in 2010 by Halvorson, a Thief River Falls, Minn., native.