A man who looks up to celebrities will never become one.
Men who look up to celebrities will never become... ones?
A man who looks up to celebrities will never become one.
Men who look up to celebrities will never become... ones?
In this instance, 'such' can be used to refer to plural as well as singular referents:
such [pronoun]
- such a person (or persons) or thing (or things)
[Collins]
such [pronoun]
- such a person or thing or such persons or things:
- kings, princes, and such
- someone or something indicated:
- She claims to be a friend but is not such.
[and, by analogy, • They claim to be our friends but are not such.]
An example of 'such' used as a formal alternative to (singular) 'one':
- And though he may possess all the faculties which go to make a skilled constructor, he will never become such without knowledge.
[Scientific American_The Constructive Faculty of the Mind; via Google]
And an example of the plural usage:
- But boys of nine are not yet slackers and loafers. It is our business to give them such an interest in life that they will never become such.
["Sir Leslie Wilson Scout Fund: Why Wolf Cubs?", The Telegraph (Brisbane, Qld. : 1872 - 1947), Tue 22 Aug 1933, Page 9. Retrieved from TROVE]
I didn't add the caveats 'dated' and 'quite formal' because the dictionaries didn't, but I certainly agree with Janus's comment.
Sometimes, the "plural" is actually one. Not a plural of course, strictly speaking, but in the example you give, one would be a very natural way of saying what you want to say:
Men who look up to celebrities will never become one.
Or, better:
Men who look up to celebrities will never become one themselves.
This is a relatively common construct, you can find many examples where a plural is used to describe a group and then the singular is still used for an individual. For instance (made up examples, not quotes):
Just because you like doctors, doesn't mean you need to become one.
Being interested in jugglers does not imply I am one!
Since the final one refers to a single individual, it doesn't need to be in agreement with the earlier plural.
In that context, you can use the pronoun them, which is not a plural form of one but an alternative, different word:
Men who look up to celebrities will never become them.
As an anaphoric pronoun, them can take the place of the word "celebrities" from earlier in the sentence, giving the meaning "Men who look up to celebrities will never become celebrities".
Compare:
in fact, we are not Spartans or Athenians, and will never become them.
(page 67; Bell, David A. “WHEN THE LEVEE BREAKS: Dissenting from the Draft.” World Affairs, vol. 170, no. 3, 2008, pp. 59–68. JSTOR, http://www.jstor.org/stable/20672809. Accessed 28 Apr. 2023.)
The word ones can't be used in your sentence, but it exists and can be used in other circumstances: e.g. "I didn't want this one, but the other ones." The Cambridge Grammar of the English Language, by Rodney Huddleston, Geoffrey K. Pullum, et al., calls "one(s)" in that kind of sentence a "pro-nominal", rather than a "pronoun": the difference is that the pronoun one found in a sentence like "One must consider many things" takes the place of a whole noun phrase, including articles (compare "The reader must consider many things"), while in a context like "the other one(s)" the pro-nominal one(s) takes the place of a noun, possibly used with a premodifier (compare "the other (red) apple(s)").
In your original sentence, "one" is neither the pro-nominal one nor the pronoun one, but actually a third type of word:
A man who looks up to celebrities will never become one.
"One" here is what CamGEL calls a determinative, and it's basically used as a stressed, independent version of the indefinite article a(n). "One" here is short for "a celebrity", like how "mine" is short for "my pen" in a sentence like "If you need a pen, you can take mine". But since the plural of "a celebrity" is "celebrities", with no determiner, I think there's no way to form an equivalent expression in the plural. CamGEL more specifically refers to this type of determinative one as "singulative one" (or "ones" for short) and says it "fills the gap resulting from the inability of a to function as fused-head", giving the example "Mary bought a book, and I bought *a/ones as well" (Chapter 5, §7.7., page 387, underlining replaced with bold).
The upvotes on terdon's answer, as well as several comments, show that a significant amount of people who visited this page think "Men who look up to celebrities will never become one (themselves)" sounds natural. I don't like that wording, because I view it as equivalent to saying "Men who look up to celebrities will never become a celebrity (themselves)", and I find it illogical to use the singular predicate "one/a celebrity" in combination with the plural subject "Men". Perhaps my attitude about this is too rigid, and it is in practice a fine way to put it. But I wouldn't choose that wording in the context of something like a grammar test: R.M.'s comment shows that I'm not the only person who finds the number mismatch problematic.
I think that in this case, you don't need a plural. Any individual man can only become 'one', so even when talking of men, each can, or can not, become one.
In this case, ending the sentence with "one" means that you're leaving off an understood, but unwritten/unspoken part of the sentence: "of them".
In many contexts, we could replace "one" with "a", but it wouldn't make sense to make that change here, unless you include a full noun to go with "a" - like "a celebrity".
A man who looks up to celebrities (a group of people) will never become one of them.
A man who looks up to celebrities (a group of people) will never become a celebrity.
After all, "a man" (literally one man) doesn't become more than one of anything, he joins a group, in this case, of celebrities.
It perhaps sounds more natural in a different context:
'Do you like these greetings cards?' 'No, I prefer these ones.'
The only pronoun here that doesn't sound awkward to me is "them":
Men who look up to celebrities will never become them.
However, this is a little bit ambiguous because it could be interpreted as meaning that the men will never become the specific celebrities they look up to, rather than become celebrities at all. (That is, will a man who looks up to Tom Hanks never become a celebrity, or will he only never become Tom Hanks?)
So I would just duplicate the word "celebrities":
Men who look up to celebrities will never become celebrities themselves.
The addition of "themselves" is not strictly necessary but it helps to emphasise that the second use of the word "celebrities" does not refer to the same people as the first one does.
"A man who looks up to celebrities will never become one of them" sort of fixes the semantics of it.
Become a man? Become one (with nature)? Become one of them.
Beats becoming ones such that they thus are.