Sharpening the tip is a task best handled by hand-stoning. Hone carefully, watch your angles and be careful not to round the tip.
If the problem is that you have inadvertently rounded the tip, you need to reform the tip. This can be done by honing a new tip shape, holding the blade at 90 degrees to the stone, modifying the curvature of the edge near the tip (sort of a modified Tanto tip), and then sharpen the edge of the new tip shape.
A flat-surface stone is best-suited for this work - not a round crock stick.
The Spyderco 'Double Stuff' ceramic stone is ideal for finer work such as this.