Charlotte Street by Danny Wallace (2011)

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Jason Priestley (not that Jason Priestley) is a little lost. He's writing for a free newspaper, living with a friend above a shop and dealing with his ex getting on with her life. He helps a girl on the street with her packages and ends up with her disposable camera and tries to solve the mystery of who she is through the pictures. 

The word stalking is used in the description but it's not quite like that.  The plot itself is quite lovely and complex and it has vivid characters--even the most minor characters are fully drawn and memorable.  This book is also filled with great self-deprecating humor like this:
"The girl with the quiff and the bottle of something blue was standing before us, staring. She had a burly friend in a denim miniskirt either side. Oh, God, I thought. There are three of them. And three of us. What if they bully us into relationships?"  (p. 118)
Priestley also spends a fair amount of time contemplating the I Saw You columns in newspapers.  I loved this lovely line: "These small moments, never said out loud, as formed and perfect as sweet little haikus, romance and longing carved out in the dust of a grubby city." (p. 144)

If you loved the quirky humor, the romance from a man's POV, and the vivid London setting of One Day by David Nicholls, you'll love this book as well.