has he written other book series apart from the former one?
The It Girl, Psycho Killer
Book series
A spin-off book series, "The It Girl", made the list in 2005.

The Constance Billard School for Girls is based on an exaggerated version of Ziegesar's own alma mater, Nightingale.

In October 2011, Ziegesar released a spin-off of her first novel: "Psycho Killer".
in gossip girl who is blair's baby daddy Prince Louis who is blair waldorf? One of the main characters of "Gossip Girl" what is gossip girl? American teen drama television series who is the director of this television series? UNANSWERABLE when did it first come out? September 19, 2007 what role does blair play in it? UNANSWERABLE are there novel series? Yes. American young adult novel series who wrote this story? Cecily von Ziegesar
Yes, "The It Girl" "Psycho Killer". "The It Girl"
Cecily von Ziegesar Cecily von Ziegesar Cecily von Ziegesar
Book series Book series Book series
 A spin-off book series, "The It Girl", made the list in 2005.
 In October 2011, Ziegesar released a spin-off of her first novel: "Psycho Killer". A spin-off book series, "The It Girl", made the list in 2005.

wiki:17789453
Cecily von Ziegesar [SEP] Book series
In New York City, while working at book-packaging firm Alloy Entertainment, she became inspired to create the "Gossip Girl" series, which presents a view of high-end teenage lifestyles. The series climbed to the top of "The New York Times" Best-Sellers list in 2002. A spin-off book series, "The It Girl", made the list in 2005. The Constance Billard School for Girls is based on an exaggerated version of Ziegesar's own alma mater, Nightingale. In October 2011, Ziegesar released a spin-off of her first novel: "Psycho Killer".