Usually software product variants, developed by copy-paste-modify technique, are often a starting point for building Software Product Line. The distinguishing factor between traditional software engineering and software product line engineering is the variability. Traceability of variability in a software product line has been recognized as crucial factor for its success. This paper presents a method based on information retrieval namely, latent semantic indexing, to establish traceability links between object-oriented source code of product variants and its FM to support conversion from traditional software development into software product line development. Tracing and maintaining interrelationships between artifacts within a software system also are needed to automate products derivation process, facilitate program comprehension, make the process of maintaining the system less dependent on individual experts.