Leila Ibraum, aged 22, was last seen on Wednesday in Loddon Spur. She left to go shopping with her friend, Radu Romedia, aged 38.
Since then, it is believed that the pair have travelled to Derby in a red Peugeot.
Investigating officer Detective Constable Abdi Awil, based at Slough police station, said: “We are working to locate Leila and Radu to ensure that they are safe.
“Although we believe they have travelled to Derby, we would be keen to hear from anyone who has any information which could help us locate them.
“If you can help, please call 101, quoting reference 43200405905.”