Next nearest coordinate from a point in alist of coordinates

Question

 Hi,

     I have a list of coordinates say {(100,30),(120,70),(300,400),(90,80),(50,60),(389,700),(690,1000),(450,300),(900,100),(1100,680)} etc

 I have sorted the list with x coordinate.. to start with a least point. 

I need to find next nearest point from a given point say (100,30).. how to find it ?  any suggestion.. do we need to find distance between two points that is nearest and compare the distance ? any idea? Thanks in advance :)