A 52-year-old man has been arrested over the alleged abduction and sexual assault of a European backpacker in South Australia's Murray Mallee region.

Police said the backpacker was being held against her will on a rural property after posting an ad on Gumtree looking for farm work.

Her family members overseas contacted South Australian police on Thursday because they were worried about her welfare.

She disappeared after heading for Murray Bridge, south-east of Adelaide.

Police said a member of the public found her on Friday and then contacted police.

Detective Inspector Greg Hutchins, of the Major Crime Investigation Branch, on Friday said her family had been informed she had now been found.

"She has obviously, potentially been through an experience and we obviously need to work out exactly what's happened," he said.

He said the man would be charged shortly.