Scopus is the best database for this type of searching, as it collates lists from several records, giving you a combined list of references, without duplicates.
Go forward in time from older articles to see who is citing them. Select a set of the most relevant articles, then click on the ... More ellipsis, and then on the View cited by link.
Go back in time from more recent articles to see who they are citing in their reference lists. Select a set of the most relevant articles, then click on the ... More ellipsis, and then on the View references link.
The results you get is sorted by Cited by (highest), but you can change this. You cannot add references from these results to your list, but you can select references, then click View cited by.
Not all the references in reference lists will be Scopus records. You can: