The Web is trying to search people’s brains.

A spate of new tech companies led by Internet stars and backed by high-profile investors is looking to leverage natural language technology, machine learning, and crowdsourcing to provide users with relevant answers to complicated questions quickly.

Their strategies vary, but the basic premise is the same: The search technology that has made Google so successful fails to access untold quantities of unpublished information typically residing in people’s heads—information that could be used for selling advertising or even sold for a fee.

“We’re working on getting all the information that people know but haven’t shared with the world on the Web and organized into a really useful resource,” said Charlie Cheever, a former top Facebook employee who co-founded Quora, a question-and-answer service with no announced revenue model that launched to the public this week. Cheever led Facebook’s hugely influential platform and connect initiatives. His co-founder is former Facebook CTO Adam D’Angelo.

Founded in late 2009, Quora generated positive buzz among Silicon Valley elites during testing in recent months.

The pre-revenue Palo Alto, California, company, which integrates with users’ Facebook and Twitter accounts and ranks experts according to user input, turned heads in March when Benchmark Capital reportedly invested $14 million at a valuation of between $85 million and $90 million.

The news came weeks after Google in February paid a reported $50 million for Aardvark, another “social search” service that taps users’ Google and Facebook contacts via instant messaging in search of answers.

The 30-person San Francisco company, since moved to Mountain View, California, launched to the public in October 2009. It was founded in 2007 by ex-Google employees Max Ventilla and Nathan Stoll with Damon Horowitz and Rob Spiro, and it is trying out sponsored answers to make money.

This year, a scholarly paper co-written by Horowitz got significant attention for its proposition of a “village paradigm” for information retrieval to supplement the “library paradigm” that underlies Google’s technology, in which answers are found in existing online content. The title of the paper echoed that of a seminal search treatise penned by Google founders Sergey Brin and Larry Page.

“Aardvark really is about connecting you to another person for a live interaction,” Ventilla said.