"The police are after us."
Terjemahan:Polisi sedang mencari kita.
They mean basically the same thing, but perhaps 'the police are after us' is a little more urgent. Like you might say 'the police are looking for the witness' to describe the police looking for someone who has not committed a crime. But the 'police are after us' suggests that we are running away, perhaps. At any rate 'are after us' is kind of like slang.