The page Deutsche Lektüre für unterschiedliche Niveaustufen by did deutsch-institut lists several books for level B2 that have been recommended by teachers. Almost half of them were published before 1980.
Here are those published after 1980 (listed in reverse chronological order):
- ErebosErebos by Ursula Poznanski (teenage fiction, 2011)
- TschickTschick by Wolfgang Herrndorf (2010)
- Die Nacht, die LichterDie Nacht, die Lichter by Clemens Meyer (short stories, 2008)
- Herr LehmannHerr Lehmann by Sven Wegener (2003)
- Tito ist totTito ist tot by Maria Bodrozic (short stories, 2002)
- Die 13 1/2 Leben des Käpt'n BlaubärDie 13 1/2 Leben des Käpt'n Blaubär by Walter Moers (children's book, 1999)
- Am kürzeren Ende der SonnenalleeAm kürzeren Ende der Sonnenallee by Thomas Brussig (not Thorsten Brussig) (1999)
The others were published before 1980 (here listed in reverse chronological order):
- Krabat by Ottfried Preußler (children's book, 1971)
- Der Räuber Hotzenplotz by Ottfried Preußler (children's book, 1962)
- Ende einer Dienstfahrt by Heinrich Böll (1966)
- Draußen vor der Tür, a play by Wolfgang Borchert (1948)
- Emil und die Detektive by Erich Kästner (children's book, 1929)
- Der Steppenwolf by Hermann Hesse (1927)
The FluentU article 4 Awesome Young Adult Books for Intermediate German Reading Practice lists four books, two of which are translations (Harry Potter, Das Schicksal ist ein mieser Verräter / The Fault in Our Stars by John Green). The two German titles are:
- CrazyCrazy by Benjamin Lebert;
- TschickTschick by Wolfgang Herrndorf (2010, winner of German Youth Literature Prize in 2011).
The article also recommends looking at winners of the German Youth Literature Prize.
The article Top 5 Novels for Learning German on the Germanica blog recommends the novels Rubinrot, Saphirblau and Smaragdgrün from the Liebe geht durch alle Zeiten trilogy by Kerstin Gier. The other recommendations are older (many of Kafka's short stories are quite readable at level B2 but were published long before 1980) or require a higher reading level (Das Parfum by Patrick Süsskind, Faust by Goethe).