I've tried 'Captivity' and 'Kidnap yaoi' topics but somehow couldn't find it. All I remember is that both uke and seme were quite young, and the seme was really charismatic. The seme also had dark hair (short/medium length). At first he was friends with/or in a relationship with the uke, before he kidnapped him and held him captive in his apartment. I think that in the end, uke's friend found out what happened and the uke was saved. It's all I can remember... Any ideas?

Scarlet? The seme's hair color doesn't match your description though.

Unfortunately that's not it but thanks for suggestion!