Pittosporum - USDA Zone 9b

[Runaround]

I have 5 Pittosporum shrubs that I planted in the spring of 2010 and newer plants that were planted spring of 2012. I wanted to see if the 2010 plants would survive the hot, hot summers we have in the San Fernando Valley area of Los Angeles. +90 degrees August, Sept and Oct. And they did beautifully. I assured that they had lots water during the summer until they got established. The 2010 plants continued to grown, however, what developed over time are long, thin, weak branches with leaves only on the end of the branches. These branches are so 'end' heavy that they droop over in a rain. The drooping seems to be permanent now.
I am looking for advice on how to prune these shrubs so that they grow strong, leafy branches.
How should I prune these plants to encourage strength in the branches?

I had planted a 'test' pittosporum in 2009 to see if it could survive the hot summers - it did beautifully! It grew strong and tall (+18 feet). I couldn't wait for the others to grow as tall and strong and form a privacy hedge on the west side of my yard. During the summer of 2012 it suddenly died. Anyone have any idea why a mature nearly full grown shrub suddenly give up the ghost?