Amidst a federal investigation into a foiled attack on a Prophet Mohammed cartoon contest in Texas, FBI Director James Comey has said that Islamic State is leveraging social media to recruit people in US.

“Hundreds, maybe thousands” of people across the country are receiving recruitment overtures from the terrorist group or directives to attack the US, he told reporters, according to USA Today.

The Islamic State, also known as ISIL, is leveraging social media in unprecedented ways through Twitter and other platforms, directing messages to the smart phones of “disturbed people” who could be pushed to launch assaults on US targets, Comey said.

“It’s like the devil sitting on their shoulders, saying ‘kill, kill, kill,’” he said amidst a federal investigation into a foiled attack in Garland, Texas, involving two gunmen allegedly sympathetic to Islamic State.

Both the gunmen, identified as Elton Simpson, 30, and Nadir Soofi, 34, were fatally shot by a police officer Sunday night after the pair’s abortive attack on the cartoon contest

Comey said Thursday that hours before the attempted Garland attack, FBI agents sent a bulletin to local authorities indicating that Simpson, may have been interested in travelling from Phoenix to attend the contest.

The FBI director, according to USA Today, declined to elaborate on why agents alerted Garland authorities to Simpson’s possible interest in the local event, though he said there was “no reason to believe he would attack or that he had left” his home in Phoenix.

Comey said the Texas case is emblematic of a larger concern facing counter-terrorism authorities related to Islamic State’s aggressive pursuit of US-based and other converts.

IS recruiters operating from safe havens in Syria are making initial contacts with recruits, mostly on Twitter, and are then “steering” them into encrypted venues where their subsequent communications are “lost to us,” he said.

“The haystack is the entire country,” Comey was quoted as saying. “We are looking for the needles, but increasingly the needles are unavailable to us. … This is the ‘going dark’ problem in living colour. There are Elton Simpsons out there that I have not found and I cannot see.”

FBI agents are working hundreds of investigations around the country involving suspected homegrown violent extremists with inquiries open in all 56 of the FBI’s field divisions, he said. “ISIL is a very popular fad among a lot of disturbed people.”