Sheppard has been charged with conspiracy to commit wire fraud, conspiracy to commit money laundering, and the intentional access of a protected computer.
Among the accounts hijacked last month included those of former US President Barack Obama, Microsoft founder Bill Gates, Amazon owner Jeff Bezos, rapper Kanye West and his wife, Kim Kardashian. The tweets offered to send $US2000 (NZ$3000) for every $1000 sent to an anonymous Bitcoin address.
One tweet from Bill Gates' account read: "Everyone is asking me to give back. You send $1000, I send you back $2000."
The NCA confirmed on Friday it had supported the US investigation and searched a property in West Sussex with officers from SEROCU, a collaboration between the Police Forces of Hampshire, Surrey, Sussex and Thames which focuses on organised crime in the south east.
It is understood that the UK has not arrested the teenager. A Government source said there was "always the possibility" the US could put in an extradition request, but would not confirm if one had been made.
However, Professor Alan Woodward, a cybersecurity expert at Surrey University, said if he were Sheppard he "would be slightly worried".
"The Americans will issue a legal assistance warrant," he said. "In this case, they did actually not just break in, but they then tried to use it for a criminal scam. They walked away with thousands of pounds. So you know, this, they were not trivial sums of money. I suspect that the British law enforcement agencies will not have a great deal of sympathy with them."
According to neighbours, Sheppard - who attended a local state comprehensive school - is "a nice lad" whose father, Mark, died about five years ago. His mother, Lorraine, had been bringing him up since her husband died.
David Anderson, the US Attorney for the Northern District of California said Sheppard "faces a statutory maximum penalty of 45 years of imprisonment" if convicted.
According to court documents, about 415 transfers were made to the Bitcoin address totalling more than $US117,000. Nima Fazeli, 22, of Orlando, Florida, was charged with aiding and abetting the intentional access of a protected computer.The Department of Justice said charges had also been filed against a juvenile. Graham Ivan Clark, 17, was arrested in Tampa, Florida, on Friday according to the Hillsborough State Attorney's Office.
It added that Clark will be prosecuted as an adult and is allegedly the "mastermind" behind the hack.
Anderson said: "There is a false belief within the criminal hacker community that attacks like the Twitter hack can be perpetrated anonymously and without consequences ... break the law, and we will find you."