Actually it is "Yuu" (and you're right) because the artist that I mentioned and looked very carefully has the all the sources of that link that I mentioned above from those images that had been copyright designed and made.
(unless "Masaru" is a typo that has been a mistake or not makes it possible for the search that has to be "Yuu", but it can be aliased to the artist so it can't be confusing for the search)
But I have a feeling "Masaru" is his pseudonym name just to hide his real first name that use to be "Yuu's" first name. Maybe.
Japanese names that are written in kanji may not be pronounced one set way. There may be multiple ways of reading the name. Unless there is furigana (see this source for instance, which indicates his name is pronounced まさる "Masaru") or the name is romanized, there is no way to tell and people are only guessing. That is the case with most of the "Yuu Yonezawa" information entered on ANN which comes from Japanese kanji credit sources.
