Is "ought to" still used?
Yes, some native speakers still use ought to, even on social media:
Pres Trump ought to see the writing on the wall, abandon proposal, roll up his sleeves & come up w/ a real, bipartisan plan to keep us safe.
Senator Chuck Schumer on Twitter
It should be noted that the to is not required in the negative:
Margaret ought not exercise too much.
Ought to can also be (very informally) written as oughta.
Is usage really declining?
Yes, I believe so. As a native American English speaker, I don't use it a lot. I prefer to use "should". A search of my text messages and other private messages (some of which is 3 years old) for ought/oughta comes up with nothing, meaning that neither me nor my friends/family use it in written communication. And I found some other sources that indicate it’s not just me.
Some grammar books don't cover ought at all:
In the Longman Grammar of Spoken and Written English, Biber et al. even explicitly exclude ought to from the discussion, arguing that it is among a group of “marginal auxiliary verbs” that “are extremely rare and largely confined to BrE”
Root Modal Uses of Should, Ought to and Be
Supposed to in Present-Day English: From Patterns
and Profiles to Proficiency Guidelines
Other sources confirm that its usage is declining:
In a recent article, Leech has drawn attention to the changing status of modals in present day use. He says: “According to an exploratory investigation we have undertaken, the English modal auxiliaries as a group have been declining significantly in their frequency of use” (2003: 223), and explicitly recommends “to those involved in the teaching of English as a second or foreign language” not to “waste hours of valuable classroom time teaching shall and ought to”
The study of modal verbs from a pedagogical perspective, quoting Leech's Modality on the Move
It even seems to be becoming less common in British English, as the Svartvik and Wright study was done on British teens in 1977:
Svartvik and Wright demonstrate that the modal auxiliary ought (to) is disappearing from the language and is being replaced by should, particularly in non-assertive contexts such as questions and negative statements.
Acceptability in Language