The girls were walking through Darnford Park at around 3pm on Monday, when the incident took place.
Staffordshire Police say it was reported that a man on a bike, who is believed to be in his mid to late 20s, exposed himself to them in the park.
Officers have released a CCTV image of a man they are keen to speak to in connection with the incident.
Pc Cameron Howard-Wight, of Lichfield's Neighbourhood Policing team, said: "We are currently carrying out extensive enquiries to identify the man in this photo.
“We take reports of this nature extremely seriously and we are urging anyone who may have been in the area at that time to get in touch as they might have important information.”
Anyone with information can call Staffordshire Police on 101, quoting incident number 794 of June 15.
Alternatively, contact Crimestoppers anonymously on 0800 555111 or at crimestoppers-uk.org