Posting via the You Boys in Green forum, the woman who calls herself Rita, said she was hoping to find a football fan that she met at the competition in France last June.
She said she has no information other than his first name Cormac and where they met.
« I’m trying to contact him about an important matter, » she wrote.
She appeals for anyone who has any ideas of how she can contact him to email her.
She explained that they met La Place du Change, Lyon – where Ireland played their Round of 16 game against France.
She describes the area as a « square in the Old Town where Irish fans gathered together on Saturday and Sunday evening during the Euros ».
The pair met at around 1am on June 27, the night after the game.
She explained: « We met while the crowd was singing « Don’t take me home, which they continued to sing for at least 10 minutes. He had lost his friends.
« If this message reaches Cormac, he needn’t worry, I just need to touch base with him about something. »