The 27-year-old woman was at a property in the Church Street area of Omagh in the early hours of Monday 28th April when she was seriously sexually assaulted.
The assault is believed to have taken place at around 2am.
Detectives are keen to hear from the driver of a silver coloured taxi who collected three females in the Church Street area during early hours of Monday.
Officers would also be keen to speak to the driver of a white coloured pick up type vehicle who stopped to assist three females in the Church Street area.
Officers can be contacted at Mahon Road on the non-emergency number 101. Information can also be passed anonymously through the independent charity Crimestoppers on 0800 555 111.