Family of missing Perth man flies to the US to join in the search

The father and brother of missing Perth man Mohammad “Naz” Rahimi have flown to the United States to search for the 20-year-old.

Mr Rahimi was holidaying in Atlanta when he disappeared more than three weeks ago.

Police in Atlanta say an investigation into the disappearance was “advancing rapidly,” they told AAP on Friday.

He was reporting missing on March 31 and was last seen on foot near the Morningside Nature Reserve and was reportedly due to return to Perth on April 11.

Mr Rahimi's friends in Atlanta have taken to social media to appeal for information, one saying she saw him in the evening, running through the nature reserve in distress.

Aria Adams said Mr Rahimi left his wallet and belongings at her home.

"He literally left everything behind ... I'm pulling my hair out from so much frustration and worry," she posted to Facebook.

Another friend said Mr Rahimi's father and brother had arrived in Atlanta to search for him on April 10.

"We won't stop looking for you. Please come back," Timothy Chima Obialo wrote.

The Australian Department of Foreign Affairs and Trade has been contacted for comment.

 (With AAP)