As the Web is becoming a powerful new medium in scientific publication and scholarly communication, citation indexing has found a new application in the digital environment. The authors reviewed the new developments in Web-based citation indexing and conducted a case study in three major citation search tools, "Web of Science", "Scopus" and "Google Scholar". Based on the evaluations and comparisons of citing reference searches, the authors concluded that there is no single solution for a complete citing reference search without a Universal Citation Digital Library. (Contains 5 tables.)