24 Girls in 7 Days by Alex Bradley

Jack Grammar, average American senior, has no date to the prom. Or so he thinks. Percy and Natalie, Jack's so-called best friends, posted an ad in the classified section of the online version of the school newspaper. They figured it couldn't hurt-after all, there's not much in this world sadder than Jack's love life. Soon Percy and Natalie have assembled a list of girls eager to go to the prom with Jack, including one mysterious girl known only as FancyPants. He has just seven days to meet and date them before he will ask one special girl to the prom.