Girls' Generation members introduce themselves in 2007 as they debut with user created content.br br Yoona was first revealed through UCC on July 6, 2007 , and over the next 8 days , all the members were revealed in that order: Tiffany , Yuri , Hyoyeon , Sooyoung , Seohyun , Taeyeon , Jessica , and Sunny . On July 16, a group video was released through UCC, and immediately after, the Girls' Generation page was opened on the official SM Town website and an official profile was also posted.