1. A method for providing a response to a user request, comprising: at a server computer with one or more processors and memory: receiving a user request from a mobile client device, the user request including at least a speech input and seeks an informational answer or performance of a task; detecting a failure to provide a satisfactory response to the user request; in response to detecting the failure, crowd-sourcing information relevant to the user request by querying one or more crowd sourcing information sources; receiving one or more answers from the crowd sourcing information sources; and generating a response to the user request based on at least one of the one or more answers received from the one or more crowd sourcing information sources.
3. The method of claim 1 , wherein the crowd-sourcing further comprises identifying, from a set of crowd sourcing information sources, the one or more crowd sourcing information sources to be queried.