A 17-year-old Northern Virginia high school student who federal authorities believe successfully helped a man make his way to Syria to fight with the Islamic State has been taken into custody, according to the boy’s neighbors and an official familiar with the case.

On Friday, FBI agents raided the Woodbridge townhouse where the teen lives with his family, leading the boy outside with his hands cuffed behind his back, neighbors said. The boy, a student at Prince William County’s Osbourn Park High School, is charged only as a juvenile, but federal prosecutors are navigating the intensive legal process to move the case into adult court, an official said.

Many details of the investigation remain unclear, but the case seems to be yet another instance of a young person living in America and using the Internet to offer tangible help to the Islamic State. Officials familiar with the case, speaking on the condition of anonymity because they were not authorized to share details, said investigators believe that the teen helped an adult not much older than himself travel to Syria. The officials said the teen helped arrange the man’s travel, in part by using online contacts that led to the Islamic State overseas.

Experts say such instances could become increasingly common as youths — inspired by well-produced terrorist posts and videos online — can now reach out and forge overseas connections.

“Social media has really been a game-changer,” said Matthew Levitt, director of the Stein Program on Counterterrorism and Intelligence at the Washington Institute for Near East Policy. “If you are drawn to or you are inspired by these things as you watch them in your mama’s basement, you can talk to somebody.”

Speaking at a congressional hearing on Wednesday, Secretary of Defense Ashton Carter said some militants in Afghanistan are adopting the label of Islamic State because of the “inspiration . . . that they crave.” (AP)

According to neighbors and a man who hired the teen to write for his Web site, the Osbourn Park student was quiet in person but exceptionally intelligent — authoring articles on complicated science and technology topics.

Dustin O’Bryant, who gave the teen a paying gig writing for his digital currency news Web site, said the boy was a “great writer” who “had a really strong understanding of the technology behind digital currency in general and even more advanced systems.” O’Bryant said he hired the teen on the spot after reading a chemistry research paper the boy wrote.

“He was a brilliant kid,” O’Bryant said. “His English wasn’t perfect, but I was willing to overlook that because the content was great.”

According to officials and neighbors, investigators conducted surveillance outside the teen’s home for more than a month before they took him into custody. Investigators also looked into another 17-year-old student at Osbourn Park, although he is thought to be a lesser player, officials said. The status of charges against him is unclear, but federal prosecutors are preparing to publicly indict the man who traveled to Syria, officials said.

The Washington Post generally does not name juveniles accused of crimes unless they are charged as adults.

Researchers from the International Center for the Study of Radicalization and Political Violence estimated recently that more than 20,000 foreign fighters have joined the Islamic State — a fifth of them from Western European nations. Director of National Intelligence James Clapper said publicly Monday that about 180 Americans have gone or tried to go to Syria since the conflict there began and about 40 have returned, although those who came back did not have nefarious motives for their travel.

Federal authorities have thwarted a number of plots. Last month, a 19-year-old Minnesota man was indicted on accusations that he tried to support the Islamic State; he had been pulled off an airplane bound for Turkey last year. Even more recently, three Brooklyn men, the youngest just 19, were arrested on charges that they planned to travel to Syria to join the Islamic State and that if that failed, authorities said, they intended to commit an act of terrorism in the United States.

O’Bryant, who lives in Alabama and talked to the teen mainly online, said the teen last reached out in February, saying that “personal matters” had taken his focus off work but that he hoped to resume writing in weeks or months.

O’Bryant said he knew that the teen was Muslim and had written online posts about his faith but did not seem to be radical. O’Bryant said he, himself, is agnostic and told the teen that he would have to keep his religion out of his digital currency articles, and the teen raised no objections.

On his LinkedIn page, the teen wrote of taking Advanced Placement classes and listed some of his interests as civil rights and social action, disaster and humanitarian relief, and poverty alleviation. He also noted his support for the Council on American-Islamic Relations of New York and Islamic Relief Worldwide.

A neighbor who declined to give her name to protect her privacy said the teen — who went to middle school with her daughter some years ago — seemed to spend a great deal of time inside his home. The neighbor said that she would see him return from school but that he rarely came out after that — even on the weekends.

“He was a pretty quiet kid,” the neighbor said.

But other than that, the neighbor said, “he was just like any other teenage kid around here.” She said he seemed to live with his mother, father, infant sister and perhaps his grandmother.

The neighbor said that on Friday, FBI agents went to both the front and the back of the family’s home, knocking for quite a while before the door opened. She said the agents emerged later with the teen. They also removed a computer and other electronic equipment , she said.

On Tuesday, a woman who emerged from the house declined to talk to a reporter. She said the family had an attorney but declined to provide the person’s name.

The neighbor said that some time after the teen’s arrest, the boy’s uncle came to the area and wondered aloud if the family had overlooked warning signs with the teen.

“They don’t understand what they missed,” she said.

U.S. Attorney Dana Boente and FBI spokeswoman Lindsay Ram declined to comment on the investigation. Ram said federal law prevented her from discussing cases involving juveniles.

Phil Kavits, a county schools spokesman, confirmed that the student, whose name he was given by a Washington Post reporter, attended Osbourn Park High School but declined to comment about any law enforcement activity. He said officials had “not been advised of any threat or risk to our students, our staff or our schools.” He added in a statement later: “There is no indication that our students are being specifically targeted to support extremist causes.”

Jennifer Jenkins and Julie Tate contributed to this report.