Q: Is there a du'a which if one reads, an angel makes du'a for the reader until the person dies?
A: I have not come across any such dua. But reading aayatul kursi in the morning, followed by the first 3 verses of Surah Ghaafir (Sura 40, in 24 Juz) will earn one the duas of 70,000 angels till nightfall, and if read during the evening, the angels make dua till morning.
And Allah knows best
Mufti Siraj Desai