Peter should develop his thesis statement during the prewriting stage. At this stage, an author thinks about what he is going to write about further down in the text, and a thesis statement is exactly that - a short summary of the main ideas that are going to be developed in a text.
The sentence should be "I had joined the soccer team to meet new friends" if you're looking for a past perfect tense verb, since this is indication it is something that is not repeated.
because you are paraphrasing the statement. in order to do that you would have to summarize the authors statement without using his words and making sure to give credit
