Verbs

3 mistakes.

There is still poeple in California who searches for gold.

poeple was just a typo, ignore it plz
All the persons of the people in that sentence, do same work and are like a unit, so why w

khoshtipAll the persons of the people in that sentence, do same work and are like a unit, so why we need to use of plural verbs?

Because 'people' is a plural word. It has the idea of 'more than one person'.

I'd heard from before that when the word "people" or simply a group, are doing a common or a joined work, we should consider them like a singular unit!

khoshtipI'd heard from before that when the word "people" or simply a group, are doing a common or a joined work, we should consider them like a singular unit!

You heard wrongly.
People is always plural.
An organization of people - company, team, rock band, etc. can be treated as singular or plural.

Thanks.