  Context: Systematic Literature Reviews (SLRs) have been adopted within
Software Engineering (SE) for more than a decade to provide meaningful
summaries of evidence on several topics. Many of these SLRs are now potentially
not fully up-to-date, and there are no standard proposals on how to update SLRs
in SE. Objective: The objective of this paper is to propose guidelines on how
to best search for evidence when updating SLRs in SE, and to evaluate these
guidelines using an SLR that was not employed during the formulation of the
guidelines. Method: To propose our guidelines, we compare and discuss outcomes
from applying different search strategies to identify primary studies in a
published SLR, an SLR update, and two replications in the area of effort
estimation. These guidelines are then evaluated using an SLR in the area of
software ecosystems, its update and a replication. Results: The use of a single
iteration forward snowballing with Google Scholar, and employing as a seed set
the original SLR and its primary studies is the most cost-effective way to
search for new evidence when updating SLRs. Furthermore, the importance of
having more than one researcher involved in the selection of papers when
applying the inclusion and exclusion criteria is highlighted through the
results. Conclusions: Our proposed guidelines formulated based upon an effort
estimation SLR, its update and two replications, were supported when using an
SLR in the area of software ecosystems, its update and a replication.
Therefore, we put forward that our guidelines ought to be adopted for updating
SLRs in SE.
