If you're looking for manga similar to Man of Many Faces, you might like these titles. All recommendations are made by Anime-Planet users like you!
Daisuke Niwa is an ordinary teenager who has a crush on his fellow classmate Risa Harada. But when Risa turns him down after he declares his love for her, Daisuke discovers the secret of the Niwa family: on their fourteenth birthday, Niwa males transform into the legendary Phantom Thief, Dark! Dark is set on stealing art and making mischief, but things become complicated when he falls for Risa's twin, Riku. As if that isn't bad enough, one of Daisuke's classmates, Satoshi Hiwatari, seems determined to capture Dark! Can Daisuke win Risa's heart, while hiding the secret of Dark and evading the police?
Both of these manga are very similar. The main characters are young boys who at night become famous thieves. They even both leave warning messages before they steal an object. They also both attend school with the person who is trying to catch the famous theif. D.N.Angel is much better, but if you liked one, I think you'd enjoy the other a bit as well.