You cannot join the Quidditch team on Pottermore.
Griffindore House Quidditch Team
There is only one Seeker on a Quidditch team.
The Bulgarian National Quidditch team
Harry plays Quidditch for Gryffindor, which is one of the Hogwarts houses.
He is the seeker on the Griffyindor quidditch team.
The Chudley Cannons!
The Holyhead Harpies.
Harry Potter played for the Gryffindor Quidditch team. Harry stayed on the team until his sixth year, when he left Hogwarts. He was picked to be captain in his sixth year.
Harry Potter played for the Gryffindor house Quidditch Team.