The Prostitutes Collective says news of two alleged sexual assaults in Christchurch on Friday night was alarming.
Prostitutes Collective regional coordinator Anna Read said police contacted her after the attacks.
"We often meet to discuss issues of violence and I think that we'll all be working together again," Ms Read said.
"It's not easy because these things happen at night time and sometimes in fairly remote situations."
Police were asking for witnesses to the two separate assaults.
In the first incident, a 21-year-old woman got into a red car and was driven to Peacock Street at about 10pm, where she was sexually assaulted.
Detective Senior Sergeant Jeremy Gunn said the vehicle was described as a shiny, new-looking red sedan, similar to a Holden Commodore, with a spoiler on the boot and a dark interior.
The man was described as Caucasian, aged about 30, with tattoos on his neck and on his thigh.
Detective Sergeant Gunn said in the second incident an 18-year-old woman got into a white van just after 10pm, believing it to be occupied only by the driver.
She subsequently realised that there were two other males in the rear of the van.