Toppik, Inc., a maker of cosmetics treatments for thin or thinning hair, is now available online at Sephora.com.     Toppik Hair Building Fibers is billed as a revolutionary way of concealing thinning hair. The product uses colored natural keratin fiber that is statically charged to bond to even the finest hair. It is undetectable to look at and is designed to withstand wind, rain and perspiration, according to the company.   “Toppik is a well kept secret among beauty professionals bec...