Some 4763 delegates are being picked for the nominating convention. 712 of those (less than 20%) are named in advance (super delegates). They include "distinguished party leaders", senators, representatives, governors, and noteworthy party members. (See chart) As of today, Wikipedia reports 420 of those 712 have expressed a preference for Hillary Clinton but they may vote as they choose, unlike the delegates who are allocated from primaries.
There's a reason why Sanders isn't getting the level of support Clinton is from Democratic Party leaders. While she has been a Democrat for decades, the same is not true for Sanders, who only caucuses with Democrats in the Senate. In fact, his Senate biography boasts that he is the "longest-serving independent member of Congress."
Not such a bad method either. Super delegates don't stop change but they reduce the likelihood that small changes in the crowd's desire will steer the boat. This is like following a four-year smoothed curve for a stock instead of following daily trading peaks and trenches.