WASHINGTON -- The FBI 's best informant has played a role in dozens of terrorism cases over the past several years and provided endless intelligence on extremists across the United States. The informant is young, rich, well-connected, easily distracted and really into reality television.

The informant's name? Twitter.

The social network is an "extraordinarily effective way to sell shoes, or vacations, or terrorism," and it puts propaganda in the pocket of kids and those with troubled minds, FBI Director James Comey said recently . "It's buzz, buzz, buzz, buzz, buzz. It's the constant feed ... the devil on your shoulder all day long, saying, 'Kill, kill, kill.'"

FBI agents have cited suspects' tweets in a slew of recent terrorism cases. Federal prosecutors have charged several Twitter users who allegedly support the Islamic State with lying to federal agents about their Twitter activity. In other cases, the FBI has pointed to Twitter activity -- including retweets -- as probable cause for terrorism charges. In one case, a 17-year-old pleaded guilty to providing "material support" to a designated foreign terrorist organization by tweeting out links.