The field of alternative small-business lenders just got a little more crowded.

Online lender Fundbox announced its official launch Thursday after securing $17.5 million in funding from a group of investors led by venture capital firm Kholsa Ventures. Like fellow startups Kabbage and OnDeck, the San Francisco-based Fundbox is aiming to carve out a niche in small-business financing by specializing in microloans. But unlike its competitors, Fundbox is targeting business-to-business firms in need of funds to clear their unpaid invoices.

The company, which was founded in 2012, provides small-business owners with loans ranging from $100 to $10,000. To apply for a loan, small-business owners connect their accounting software to accounts on the company website. Customers then select the unpaid invoice for which they would like to receive a loan. Fundbox analyzes the level of risk posed by each invoice by pulling data on the small business's financial condition and customer demographics, as well as other information like the impact of seasonal patterns. Customers pay back the loans, which carry fees comparable to the interest rates charged by credit card companies, over 12 weekly installments.

Fundbox began making loans in August 2013 and has attracted a number of high-profile backers, including former Citigroup chief executive Vikram Pandit and Jay Mandelbaum, JPMorgan Chase's former head of strategy and business development.

Fundbox is one of several alternative lenders that has attracted interest from investors of late. Kabbage announced Wednesday that it has received $270 million in financing from institutional investors, just one year after receiving a $75 million credit facility. OnDeck, which has made $1 billion in loans since its founding in 2007, received $77 million in new funding in March.