Mark evens is a nobody. He is just a passby character that Rowling said had the same name as Harry's mom and that she didn't notice until after the fifth book was published. Read on page 13 (U.S version) and page 17 any other version I think. It was just a character that Dudley beat up with his friends one night with his gang.
So don't worry about this character. J.K. Rowling already dismissed this option from the very long list of people that the HBP could be!!!
Yeah, she said that quote,"Mark Evans, a 10-year-old boy mentioned in passing in Harry Potter and the Order of the Phoenix (book 5) has no significance to the series. The fact that he shares a last name with Harry Potter's mother, Lily Evans, is purely coincidental and unintended." (Source: JKRowling.com.) Maybe she made him up just so people would quesion it. Who knows? Except that Mark Evans is definitely not the HBP.