Dozens of Twitter accounts. Thousands of media-savvy followers. Slick propaganda videos. The Web-based branding efforts of the extremist group the Islamic State show that they're waging a war online as well as on the ground in Iraq and Syria.

A PRICE has been put on the head of a US citizen believed to be the mastermind behind the Islamic State’s startlingly strong propaganda blitz.

A year ago the FBI issued a $53,500 reward for information leading to the capture of Ahmad Abousamra. Now, he’s believed to be a key part of the Twitter and YouTube propaganda campaign which so graphically proclaims the Islamic State’s views and actions to the world.

“There continues to be a worldwide search for Abousamra and he will be pursued until he is found,” FBI Assistant Special Agent in Charge Kieran Ramsey told ABC News.

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Abousamra, 32, and formerly of Stoughton, Wisconsin, was a honour-roll computer science student in Boston.

After returning from a trip to the Middle East in 2004, he was questioned by the FBI’s Joint Terrorism Task Force in 2006.

He fled to Syria shortly after.

Since then, he “has shown that he wants to kill United States soldiers,” the FBI says.

The case being compiled against Abousamra includes the allegation he had worked with the “media wing” of al Qaeda in Iraq before the unit evolved into the Islamic State.

He has continued his old job within the new organisation, the FBI says.

The Islamic State, sometimes referred to as ISIS or ISIL, used dramatic footage and pictures on social media to spread fear by claiming responsibility for the beheading of two US journalists and the brutal massacre of both civilians and soldiers who have opposed its incursions into Iraq.

The quality and refinement of the propaganda presentations has received widespread attention.

Abousamra has outstanding warrants for his arrest in the US relating to conspiring to support terrorists, conspiring to murder American soldiers and for making false statements to police.

He is believed to have travelled to Pakistan in 2002 in to receive training “in order to fight and kill American nationals,” prosecutors say.

He later came to the attention of authorities for working with Tarek Mehanna who has since been convicted with conspiring to conduct a terror attack within the US.

Mehanna and Abousamra allegedly spent much of their time watching jihadi videos “as a source of inspiration to personally engage in violent jihad and martyrdom”.

Prosecutors say the pair planned to buy automatic weapons for an attack on a US shopping mall. They also allegedly schemed to assassinate two US executive-branch government officials.

The prosecutors allege Abousamra liked to use code words such as “culinary school” when referring to terrorist camps and “peanut butter and jelly” when referring to jihad — or holy war.