What are ways I can look for someone missing online if I’m not a private investigator or job related to this? He’s been missing for 4 days already.

Happened to me in varsity, my classmate went awol for 4 weeks. Didn't answer his phone or texts. I got hold of his listed next of kin(his mom) from the registrar and i sent her a message, and she replied that he went back home for a bit, he needed some personal time away from varsity.

So yeah, find the contacts for their family and check in with them

If it is an adult, the police probably won't do much. If they are at home but not communicating, you could request the police go there to do a welfare check. I don't know what that entails, I know they cannot just go kick down the door though.

...do you mean it's a person whom you typically notice online who has been gone for 4 days,

or a person you know irl who has been gone for 4 days?

Idk that you should

maybe if you look into some osint tools.