What is the best way to report an account that is obviously being boosted?

I'm not talking about a smurf. I'm talking about someone's account that has been Bronze or low Silver for months and then all of a sudden the account has a 95% winrate over the last 30 games and the D/F summoner spell order is reversed. Like, super obvious and the guy is linking his op.gg in champ select to get the role he wants.

Where should a report be sent? I don't want to be lame and name the account here because I could just be some random psycho trying to sully someone's name/