Live Wire by Harlan Coben

Sports agent Myron Bolitar is asked by his client, former tennis star Suzze T, to find her husband, rock star Lex Ryder. Lex has run off because a Facebook post has insinuated that their unborn child is not his. While trying to find Lex, Myron sees his sister-in-law, Kitty, who disappeared with his brother, Brad, over fifteen years ago. Myron and Brad have been estranged since then and Myron wishes that they could reconcile after all this time. But he discovers that the past is still relevant--in more ways than one.