Sophia Gourlay and Laura Walker were last seen around 6.20 am on Tuesday in Lochwinnoch.
It is believed that they boarded a train in the direction of Glasgow city centre.
Sophia has been described as 5ft 6in tall with long dark brown hair.
She was wearing a black duffel jacket with black hood, black trousers and dark trainers.
Laura is described as 5ft 1in tall with mouse blonde hair and she was wearing a black North Face hoody, grey jogging bottoms and white/black trainers.
In a post on social media, Police Scotland wrote: “Officers in Renfrewshire are appealing for the public’s help to trace two teenage girls reported missing from the Lochwinnoch area.
"Anyone who may have seen Sophia or Laura since this time, or has any information on where they might be, is urged to contact Police Scotland via 101 quoting incident number 2723 of 28 September.”