A person who owns a part of something with other people.
A sharer is someone who has a part of something with other people, like a toy or a cake.
Examples:
She is a sharer of the cake.
The sharer of the toy is happy.
The sharer has a piece of the cake.
The sharer of the pizza gets a big piece!
The sharer of the treasure gets a lot of gold.
The sharer of the secret tells everyone.