She was found dead on the pavement next to a skip on a street in Croydon, Surrey, after neighbours heard her screaming in the early hours of Sunday morning.
Three men, aged 20, 25 and 26, were yesterday arrested, but the older two were later bailed to return to a London police station on 12 October. A man was then arrested in the early hours and the two were being questioned today.
The teenager, who had described herself as the "happiest girl in the world", dreamed of becoming a supermodel. She had attended the Brit School for the performing arts in Croydon where other former pupils include music stars Morcheeba, Amy Winehouse and Katie Melua.
After taking part in the Swatch Alternative Fashion Week in April this year, and before recent revelations about Croydon-born Kate Moss's private life, she said: "I would love to be compared to Kate Moss because she is just so amazing. To be where she is one day would be brilliant."
Detective Chief Inspector Stuart Cundy, leading the investigation, confirmed she had been working as a model but said: "Whether that has anything to do with the attack we really don't know at this time."
He said: "As far as we are aware there are no injunction orders for people to stay away from her."
Police were last night examining CCTV footage from Saturday night of Sally Anne out with friends in Croydon. Officers are searching for a murder weapon in nearby gardens.
Her stepfather, Stephen Chiddy, and two stepsisters Michelle and Nicole visited the scene yesterday. Her parents, Linda Chiddy and Steven Bowman, have appealed for help in tracing the killer.
The family said in a statement: "We love and miss her so much and wish to stress that if anyone has the slightest information about Sally Anne's death, even if they don't think it is important, please come forward."Reuse content