Matthew Cronjager, 18, of Ingatestone, Essex, tried to get hold of a 3D printed gun or a sawn-off shotgun to kill his target, the Old Bailey heard.
He shared patriotic propaganda and explosive-making manuals online, BBC News reported.
He admitted having "terrorism publications" but denied other charges and was convicted by a jury.
He shared material with like-minded people he had met on the web - which included an undercover officer who had infiltrated a Telegram group called The British Hand.
His lawyer Tim Forte told jurors that while Cronjager accepted sending "vile" messages, in reality he was nothing more than a "keyboard warrior".
"He was the outsider, he was the other," he said.
In November last year, Cronjager suggested setting up a collective PayPal account to buy weapons and other items for the group.
Referring to his friend, he told the undercover officer: "I've found someone I want to execute. I figure we could just 'find' a double barrel shotgun and saw it down for things like this."
Police seized a large amount of material demonstrating his commitment to an "extreme right-wing cause" when they arrested him at his home in December.
Prosecutor Alistair Richardson told jurors the defendant had given "pretty close to a full admission of the offences" when faced with the "overwhelming evidence of his own messaging".
The jury found him guilty of preparing acts of terrorism, and disseminating "terrorist publications" on Telegram.
He was remanded in custody to be sentenced in October.