"Information posted to social media websites is publicly accessible and voluntarily generated. Thus the opportunity not to provide information exists prior to the informational post by the user," it says.
It says the application should provide information about possible domestic and global threats superimposed onto maps "using mash-up technology".
The bureau has asked contractors to suggest possible solutions including the estimated cost.
Privacy campaigners say they are concerned that the move could have implications for free speech.
The FBI's Strategic Information and Operations Center (SOIC) posted its "Social Media Application" market research request onto the web on 19 January, and it was subsequently flagged up by New Scientist magazine.
The document says: "Social media has become a primary source of intelligence because it has become the premier first response to key events and the primal alert to possible developing situations."
It says the application should collect "open source" information and have the ability to:
Jim Giles, consultant
The US Federal Bureau of Investigation has quietly released details of plans to continuously monitor the global output of Facebook, Twitter and other social networks, offering a rare glimpse into an activity that the FBI and other government agencies are reluctant to discuss publicly. The plans show that the bureau believes it can use information pulled from social media sites to better respond to crises, and maybe even to foresee them.
The information comes from a document released on 19 January looking for companies who might want to build a monitoring system for the FBI. It spells out what the bureau wants from such a system and invites potential contractors to reply by 10 February.
The bureau's wish list calls for the system to be able to automatically search "publicly available" material from Facebook, Twitter and other social media sites for keywords relating to terrorism, surveillance operations, online crime and other FBI missions. Agents would be alerted if the searches produce evidence of "breaking events, incidents, and emerging threats".
Agents will have the option of displaying the tweets and other material captured by the system on a map, to which they can add layers of other data, including the locations of US embassies and military installations, details of previous terrorist attacks and the output from local traffic cameras.
The document suggests that the bureau wants to use social media to target specific users or groups of users.