The incident was reported to have happened in the Magazine Street area of the city in the early hours of Sunday, November 10.
The victim was standing outside licensed premises between 1am and 1.25am when an unknown man approached her from behind, grabbed her face, and out his arms around her while kissing her on the cheek and touching her inappropriately.
The man is described as white, with brown hair, facial hair, a slim build, and around 5 foot 8 in height.
He was wearing a white shirt with dark trousers that were possibly jeans, and white trainers.
A PSNI spokesperson said: “Police appeal to anyone who witnessed what occurred, or who helped the victim, to call them.
“Police are also keen to hear from motorists, including any taxi drivers, if they have dash cam footage from the area at this time.
“Officers also urge anyone who thinks they may know the male to contact them.”
Police deployed extra officers to patrol Derry following four reported sexual assaults in the city at the end of October and the beginning of November.
The attacks were raised at the Stormont Assembly by Foyle SDLP MLA Sinéad McLaughlin, who said of violence faced by women and girls:
“This is not just an issue for women alone,” said Ms McLaughlin.
“It is our shared responsibility.
“We need to stamp it out.”