How do I reference an article that’s mentioned in an article I read?
That's called a secondary citation. Here's the APA guideline:
General Format:
In-Text Citation (Paraphrase): (Author Surname, Year qtd. as cited in Author Surname [of the source you read], Year)
Reference: Author Surname, First Initial. Second Initial [of the source you read]. (Year). Book title: Subtitle. Publisher.
Example 1:
In-Text Citation (Paraphrase): (Fong, 1987, as cited in Bertram, 1996)
Reference: Do not include Fong (1987) in your References; do include Bertram (1996).