When they say there's a youth movement in Hollywood, they don't mean a surge in cosmetic surgery. A bumper crop of teen-to-twentysomething stars has worked its way into the hearts of teens through movies and TV by being both charming and cheap. But People Pop Profiles surveyed a sample of stars against a sample of college-age consumers to see how deeply they have their hooks in tomorrow's mass market. "Scream" has been good to Neve Campbell, a true icon among young adult consumers. Jennifer Love Hewitt, the marquee name in Sony Corp.'s lackluster "Can't Hardly Wait," rates as fun and intriguing. Her "Party of Five" co-star Scott Wolf can howl over his coolness, but sags in stylishness and in uniqueness. "Titanic" star Leonardo DiCaprio was dripping with cool and sexiness. And "Buffy the Vampire Slayer's" Sara Michelle Gellar's contemporaries would kill to have her up-and-coming scores.