Boris Johnson has asked Donald Trump to "reconsider the US position" to grant immunity to the suspect Anne Sacoolas, after the death of Harry Dunn.
Downing Street said the two leaders spoke on the phone after the parents of Harry Dunn expressed their "anger and frustration" over how the death of their son had been handled by the UK government.
A Number 10 spokesman said: "The Prime Minister urged the President to reconsider the US position so the individual involved can return to the UK, co-operate with police and allow Harry's family to receive justice."
They said: "The US President said he was fully aware of the case and deeply saddened by what has happened, and he expressed his condolences to Harry's parents."
"The leaders agreed to work together to find a way forward as soon as possible," they added.
The 19-year-old died on August 27 after his motorbike crashed with a car close to RAF Croughton in Northamptonshire, a military base used by the US Air Force.
The suspect in the case, 42-year-old Anne Sacoolas, reportedly married to a US intelligence official, was granted diplomatic immunity following the crash.
The Foreign Secretary said the Government was "continuing to press US authorities" to allow police to follow up their inquiries into the motorcyclist's death.
The family had previously criticised Dominic Raab's approach to their meeting on Wednesday as a "publicity stunt".
Mr Raab said: "I share the frustration of Harry's mother and father. They have lost their son and the justice process is not being allowed to properly run its course.
His mother, Charlotte Charles, said earlier: "There has always been another gut feeling in our tummy that something is not right."
She said: "We've always had an extra feeling over the top of that utter awful nausea feeling that you get every morning when you wake up when you realise you've lost your boy."
Speaking after the meeting with Dominic Raab, Harry's mother told reporters she felt "let down by both governments" and had no answers.
She said: "I can't really see the point as to why we were invited to see Dominic Raab. We are no further forward than where we were this time last week.
"Part of me is feeling like it was just a publicity stunt on the UK government side to show they are trying to help."
Earlier the family lawyer Radd Seiger said: "To say we are disappointed with outcome would be an understatement."
"We are frustrated. We are angry," he added.
Mr Raab met Harry's mother, Charlotte Charles, and father, Tim Dunn, on Wednesday afternoon after having talks with US Ambassador Woody Johnson on Tuesday.
The prime minister, Mr Raab and Northamptonshire Police have asked the US to consider waiving the immunity.
It has since emerged that Mrs Sacoolas was previously handed a fine for "failure to pay full time and attention" while driving in the state of Virginia in 2006.
Northamptonshire Police Chief Constable Nick Adderley said US authorities had been appealed to in "the strongest terms" to apply a waiver and "allow the justice process to take place" after Mrs Sacoolas left the UK despite telling officers she did not plan to do so.