The 38-year-old was walking in Wordsworth Road on Saturday (December 20) when she was attacked between 10.15pm and 10.45pm
She was approached by a man and threatened with a knife before he stole property, including a mobile phone and MP3 player, and sexually assaulted her.
The suspect has been described as white, in his 20s, about 6ft 2in tall, of proportionate/stocky build, with an angular face, clean shaven, with shaved dark hair. He was wearing a grey hooded top and grey trousers and was hanging around by the public phone box situated at the junction of Rowlands Road and Wordsworth Road shortly before the incident happened.
Detective Constable Tony Taylor, from Worthing CID, said: "After the assault happened the victim made her escape and the offender ran away into Rowlands Road.
"We believe that there were other people in this area at the time and their attention may have been drawn to this man.If anyone thinks they saw or heard anything suspicious then we would urge them to contact police on 0845 60 70 999, quoting serial 1884 of December 20, or Crimestoppers anonymously on 0800 555111."