How can I contact this guy?

So,there is a guy in warframe market that sells a riven I want,and it says he's online in game but he's not and I've been trying to contact him through multiple ways but nothing. Is there a way to contact him besides the game or the market? I can't ask someone of his clan as I can't link his clan in chat and see the members soooo....damn. :( Any suggestion what to do?(I already checked other rivens and no,there are no similars,he's the only one selling THAT riven lfmao)