Human-powered search startup ChaCha has overtaken Google to become the most popular SMS search service in the US following "explosive growth" in the use of its mobile product, according to Nielsen Mobile. The company shot from a market share of just 7% in early 2009 to 28% less than three months later, a growth rate of more than 800%. Nielsen says it now has more text traffic than Google, coming from users predominantly under the age of 25.

ChaCha, which launched in 2007, offers a free service that lets mobile users ask any question in English and receive an answer by SMS in a few minutes. It also has a website where it publishes the queries it has so far answered, more than 300m to date. The company says it now receives around 1m questions a day and has more than 14m users a month.