Everyone at page 14 (labelled 13 on page) staring at the imaginary camera, cause we are all thinking the same thing in terms of the culprit.
Well, chapter one introduces a protagonist, some suspects and an as-yet-unidentified evildoer, as in a traditional mystery novel. And yeah, Yukia is definitely drawn to resemble Clownman, with that pointy chin and weirdly high forehead. He seems a bit odd and out of step with the group, too. He might even have a motive, in that he's the oldest of Toraji's mangaka friends, yet lags behind the rest professionally. Then again, Izou looks almost cartoonishly evil and clownlike when introduced on page 13, and he's wearing a beanie, as if to conceal hair loss.
Toraji's editor, Eichiro, seems quite suspicious as well, and he arguably resembles Clownman most of all. He's got not only the chin and forehead, but also the wide cheekbones, jug ears and muscular physique. Still, I think you're right: Yukie's calm demeanor and spooky vibe put him way out in front among our first batch of suspects. The real killer is almost always introduced early in stories like this, so...