The first incident took place around 2.55pm on Tuesday 4th September when a man, believed to be driving a grey car, approached a 15 year old girl as she walked home from school down Livesey Branch Road in Blackburn.
Police suspect the same man may be responsible for both incidents and are appealing for information.
The man is described as white, aged in his 20s to 30s, driving a dark grey or black car.
DC Will Hogan from South Ribble CID said: “These are two very concerning incidents which have left both girls very distressed. It is possible there may be other victims that this man has exposed himself to, so I would appeal to anybody that thinks they have seen this man or with any information that could assist with our investigation to come forward.”