The suspect in the crash which killed Harry Dunn is “wanted internationally” after an Interpol notice.
Mr Dunn 19, died after a crash in Northamptonshire in August and US national Anne Sacoolas is suspected of causing his death by dangerous driving.
A Home Office extradition request was rejected by the US in January.
In an email from police to Mr Dunn’s parents the force said “the wanted circulations should be enacted” should Mrs Sacoolas leave the US.
Reacting to the news Mr Dunn’s mother Charlotte Charles said: “It’s been a terrible time for us. We are utterly bereft and heartbroken and miss our Harry every minute of every single day.”
She said the latest development was “important news” and the family were “in pieces”.
“I just want to urge Mrs Sacoolas to come back to the UK and do the right thing,” she said.
“Face justice and maybe then our two families can come together after the tragedy and build a bridge.”
Motorcyclist Mr Dunn died in a crash with a car near US military base RAF Croughton on 27 August.
Mrs Sacoolas, the wife of a US intelligence official, claimed diplomatic immunity and returned home.
The 42-year-old was charged with causing death by dangerous driving in December, but an extradition request was rejected.
An Interpol Red Notice – a request to law enforcement worldwide to locate and provisionally arrest a person pending extradition, surrender, or similar legal action – has now been issued.
On its website, Interpol states a red notice “is an international wanted persons notice, but it is not an arrest warrant”.
The prime minister’s official spokesman said the government had “worked throughout to try to get justice for Harry Dunn and his family and we have been clear throughout that Ann Sacoolas should return to the UK to face justice”.
He said the UK Government had made it clear to the United States and to President Donald Trump that it considered the rejection of an extradition request for Mrs Sacoolas to be ” a denial of justice”.