Most teens don't know it, but they love epistolary novels. Those are the books written as letters or other documents.

By revealing a plot through letters or diary entries, authors offer readers direct access to the inside story. Reading someone else's journal or mail opens an intimate window into the character's life, actions and emotions.

Novels in letters have been popular for decades -- even centuries. These days, changing technology keeps authors on their toes. Today's teens don't write letters, and for many of them even e-mail is passe.

They text, IM and use social networking software to keep in touch. They don't keep a diary; they blog. Authors need to do the same.

Melissa De La Cruz's "Angels on Sunset Boulevard" (Simon & Schuster, $15.99, 13 and up) incorporates new technology in an intriguing way. TAP -- The Angel's Practice -- is a MySpace-esque social networking site, a pleasantly intoxicating drink and the center of every young Los Angeleno's life.

If you're popular on TAP, you're famous: People send you expensive gifts, you're invited to the most exclusive parties ... and you have a very good chance of disappearing off the face of the Earth.

That's what happens to Johnny Silver, TAP superstar who's become a real-life rock star. He disappears off the stage at a concert, at about the same time the younger sister of TAP-popular (but not legendary) Nick disappears from a TAP party. When Nick begins to investigate, he learns that his new love interest, Taj, may know more about the mystery than she's letting on.

The TAP pages that start each chapter separate this mystery for older teens from the pack. Listing bands, books, friends and wish lists, each TAP page gives more life to the characters. The evolution of the TAP pages reveals plot points that are not apparent in the text. In "Angels on Sunset Boulevard," TAP is another character -- and a truly fascinating one.

Less successful is Shana Norris' "Something to Blog About" (Amulet Books, $15.95, 10 and up). Libby Fawcett is a klutzy sophomore who starts a blog after she burns half her hair off during chemistry class in front of the boy she's had a crush on since eighth grade. Of course, she makes her blog password protected so no one can read it.

In her blog posts at the start of each chapter, she spills all: her love for Seth, whom she agrees to tutor in chemistry even though she's practically failing; her cousin's quest to win the heart of her best friend; her hatred of Angel Rodriguez, whose dad happens to be dating Libby's mom.

When Libby's mom invites Angel and her dad over for dinner and Angel steals the password to Libby's blog, all of Libby's secrets are out. Will her friends forgive her? Will Seth? Will everybody ever stop laughing at her?

Predictable and unrealistic, "Something to Blog About" still manages to be a somewhat entertaining read for younger teens. Alternating between blog posts and traditional first-person narrative, Norris creates a charmingly naive teen existing in a stereotypical high school world.

The blog environment saves this novel from being entirely trite, but for better "Oh no, my secret blog/diary/journal has been released in the world!" stories, try "The Secret Blog of Raisin Rodriguez" by Judy Goldschmidt (Razorbill, $5.99, grades 5-9) or "How My Private Personal Journal Became a Bestseller" by Julie DeVillers (Dutton, $5.99, grades 5-8).

Without a doubt, the best of the current novels exploring alternate formats is "My Most Excellent Year: a Novel of Love, Mary Poppins, & Fenway Park" by Steve Kluger (Dial Books, $16.99, 13 and up). Like Mary Poppins, "My Most Excellent Year ..." is "practically perfect in every way," from its characters to its crazy, convoluted plot and everything in between.

The story is told entirely in e-mails, texts, IMs, diary entries and the occasional transcription of a conversation among a trio of characters, their parents and a few additional people. This is a true polylogic epistolary novel, one with input from more than two characters.

The frame of the story is an assignment given to our three main characters at the end of their junior year of high school. Each must write about their "Most Excellent Year." All three write about the adventures, relationships and heartache of the same year.

T.C. (Anthony Conigliaro Keller, named after a baseball player) is a rabid baseball fan whose mother died of cancer when he was young. Augie is T.C.'s gay Asian-American "brother" -- they adopted each other when they were 8 -- who loves soccer, swimming and musical theater.

Ale is Augie's new friend, the daughter of a Mexican diplomat who would rather be an actress than a politician but can't tell her parents. T.C.'s in love with Ale; Augie's in love with soccer teammate Andy; Ale is pretty sure that she can't stand T.C. She's wrong.

So much happens in the course of this novel that it's difficult to provide a synopsis. It has a friendship between T.C. and a deaf 6-year-old and a whirlwind trip to New York City to meet Julie Andrews. There's a very memorable expedition to the zoo, a couple of theatrical spectaculars and a plot to build a baseball diamond at Manzanar.

Yet the story is remarkably easy to follow, the characters are believable (if extraordinarily lucky), and everything fits together perfectly. In fact, it had this reader in tears at the end -- not because it's sad (it's not), but because it's just so darn great.

Whatever the format, whatever the plot, a novel must be engaging. Epistolary novels allow the reader to interact with the characters in a new way.

For more recommended books written in alternate formats, check out "Dear Diary," a booklist created by Carnegie Library of Pittsburgh teen librarians.