The visitor, who does not wish to be named, is currently staying with friends in the city.
She said she was astounded by the antisocial behaviour taking place on 400-year old structure.
Her comments come as video footage of youths drinking on the Walls has been posted on internet video sharing site YouTube.
The 33-second clip shows two young men racing to down bottles of spirits, while being goaded by friends.
Having finished their alcohol, the pair discard the bottles by smashing them on the Walls.
The American visitor said the footage was indicative of what she witnessed when visiting the Walls on Saturday.
"There were gangs of teens all over the Walls and I found it very off putting.
"I had hoped this would be the highlight of my trip but I felt uneasy.
"It would be much more attractive to tourists if these guys and their alcohol weren't around."
A spokeswoman for Derry City Council said the council was involved in tackling ongoing difficulties on the Walls.
"The Council and the Derry Visitor and Convention Bureau continues to work with venues and event organisations to continue with the Business Animation Project to further promote the Walls as a tourist destination.
"The reduction of anti-social behaviour in the city requires a multi-agency solution and Council will continue to work with the Civic Alcohol Forum, community organisations and the Community Safety Partnership to redress any issues of concern."
She said the council remains committed to investing in the visitor experience and promotion of the historic city walls.

To watch the youtube clip click here