Links dealing with the magazine are here and here. The latter is to the German Wikipedia site, but you can click on a button for a rough translation to English. It is useful for a listing of contributors to the publication.
A brief discussion of Jugendstil is here, and the Wikepedia entry on Art Nouveau, with a section on Jugendstil, is here.
Below are some Jugend covers, the earliest from the time they embodied Jugendstil, and one from later on when Art Nouveau was passé and Weimar culture reigned. One detail that interests me is that the magazine's covers in the early years differed dramatically, depending on the style and taste of the artist doing the cover illustration. Moreover, there seems to have been no set Jugend logotype; the cover artist supplied his own typography.