A man is reported to have approached the girl on the canal path, near the Morrison’s car park, and sexually assaulted her between 7.30pm and 8pm on October 1, Dyfed-Powys Police said.
He is also alleged to have followed her to the Bron Gungrog area, on the other side of the town.
Officers have also received a second report of a man following a woman to Salop Road shortly afterwards and approaching a woman near the Applegreen garage, when he made some unsolicited comments.
A suspect has been arrested, charged and remanded into custody but police are now appealing for further information regarding the incidents.
Anyone with information that could help officers with their investigation is asked to report it to Dyfed-Powys Police, either online, by emailing firstname.lastname@example.org, or by calling 101.