The online petition demanding the rapper's release has attracted more than 390,000 signatures since his arrest last Sunday.
Celebs including Meek Mill, Cardi B and Offset have joined Jay-Z in condemning his arrest by immigration officers - who claim the British-born artists is in the US illegally.
Savage's legal team - who say he has a visa application pending - have said a gun reportedly found in a car he was driving when he was arrested does not belong to him.
Earlier this week, US reports said the musician was in a car that was driving recklessly and a loaded pistol was found in the glove compartment after his arrest.
Lawyer Brian Steel said: "That was not his car and the gun retrieved is not his. No one will be falsely accusing my client. 21 Savage has done absolutely nothing wrong."
Savage, whose real name is Sha Yaa Bin Abraham-Joseph, moved to the States aged 12 in 2005.
His lawyers say his legal immigrant status expired in 2006 "through no fault of his own" and he should be eligible to fight his removal from the country in court.