A survey of stars known to possess planets shows the vast majority to be severely depleted in lithium.
Scientists think events early in the star's formation may be responsible for producing the lithium phenomenon. 
Researchers who have studied meteorites with compositions unchanged since the beginning of the Solar System say the element's presence in our star ought to be 140 times greater than is observed.
Another approach is to monitor a star for extended periods in the hope a planet will pass across its face. This transit reveals the planet's presence by making the star's light dim ever so slightly. 
http://news.bbc.co.uk/2/hi/science/nature/8354522.stm