Can be said to people you know its casual or familiar I wouldn't say it to a bunch of strangers. Its similar to the American "HI Folks."

For formal situations and, when meeting strangers, "Hello" works well. Among adults in my social circle, I never hear "Hi people." I sometimes hear "Hi everybody." I do hear "ayyyeee," "ayyyeee peoplezzz," and "Hi people," among the teenagers at the mall. I imagine that in 50 years the English textbooks will say "Hello" is archaic and that the suggested greeting for formal situations is "ayyyeee peoplezzz."

Saying 'hi people' is a bit weird. Nobody says that. A 'hi' on its own should suffice. To me, 'hi people' is strange because I am already aware I'm a person, you saying it might suggest that you're not a person haha. You could say 'hi everyone' if you wanted to, but you need to have about 4 people for that to work.

This question is interesting because you made me realize I rarely say hi to people. I text it but rarely say it. With that being said I don't think it's awkward or not natural... I think it's a little more feminine. Nothing wrong with it but I think a hey or hello sounds better. Just my opinion and hopefully some other people add their own thoughts!

As Bill says, informal, friendly, people you know. Not strange. As Bill says, like Hi folks. Hi guys. Hi friends. Greetings. It's just an opening. Be ready to follow it with something.