A woman with learning difficulties who went missing last week told police she was sexually assaulted in Forest Hill.
Police are now appealing for anyone who may have seen the victim and the suspect in the area to come forward.
The woman, who is in her 20s, was reported missing during the evening of Sunday, December 27.
She returned home in the early hours of the following day, with an unknown man.
After he had left, she later alleged he had sexually assaulted her after taking her to his flat in Forest Hill, between midnight and 4.30am. It is not known how they met.
Officers are now trying to trace him. He is described as a black male of slim build, around 5ft10, and aged between 25-30.
He was reportedly wearing a black coat, black tracksuit bottoms and white trainers.
Officers are keen to hear from anyone who saw a man matching that description walking in the Forest Hill area, with a woman, between midnight and 04:30hrs on Monday, December 28.
Anyone with information is asked to call 101 quoting the reference CAD 935/28DEC20.
Alternatively, information can be provided anonymously by calling Crimestoppers on 0800 555 111.