San Francisco-based HealthTap announced this week that it had raised $24 million in its second round of funding. Khosla Ventures led the investment with return backers Mayfield Fund and Mohr Davidow Ventures contributing, too. As part of the deal, Khosla Venture's Keith Rabois and former Square COO will join HealthTap's board of directors. Vinod Khosla will join as an advisor, too.

HealthTap’s core offering is a question and answer platform that helps users find health information written by physicians — both online and through the mobile apps. It has also added physician ratings and a data insights feature that helps users better understand doctors' referral patterns to find doctors their doctors trust.

HealthTap now counts more than 38,000 physicians as part of its network -- marking a near quadrupling over the past year, the company says. It also claims that it serves "tens of millions of people worldwide" through its website and apps.

HealthTap plans to use the funds to build out its web and mobile offerings and build out its team.

“In its current state, our healthcare system is expensive, difficult to access, and error prone,” Vinod Khosla, founder of Khosla Ventures stated. "The future of healthcare is at the confluence of big data, smart algorithms, and simple-to-use interfaces that will provide amplification of our MD's resources: HealthTap is breaking ground in all three, and we’re excited to help them make their compelling vision a transformative reality.”

At the mHealth Summit last year Khosla made a number of provocative statements about healthcare:

“The right way to look at it is to say ‘How does innovation happen and how do very large systems like the healthcare system change?’ Most of the time change comes from the outside. Not the inside where there are too many vested interests, too many people with very good intentions who have too much experience to be unbiased,” Khosla said at the time. “They are not naive enough to ask naive questions. The answers have changed because of the circumstances — because of technology. Healthcare innovation will be consumer-driven not doctor-driven. It will be driven by devices that power the consumer to have better data about themselves.” Khosla was quick to point out that technology is an important component but not the only one: “It is necessary but not sufficient.”

Since the beginning of last year, Khosla Ventures has made a number of investments in digital health companies, including Ginger.io, Cellscope, AliveCor, and Misfit Wearables.