Question

How was Augustine influenced by Neoplatonism?

Answer 1

Certainly, by the time he wrote the Confessions, Augustine had read some Plotinus and become much influenced by his style and arguments.
This is evident in the Confessions, both in the persistent series of questions with which Augustine pursues a difficult problem (as in Confessions 1.3.3-4.4), and in occasional flashes of exhortation (as at Confessions 1.18.28). Neo-Platonism influenced in Augustine his entire concept of God and of Creation. In the Neo-Platonist view, all things (including souls) had an infinite, timeless, and unchangeable God as the cause of their existence. Neo-Platonists held that everything existed only to the extent to which it participated in God. Plotinus taught that a person must turn inward to find God, who is identical with the inner reality of the soul. 

Answer 2

Neoplatonism was a major influence on Christian theology throughout Late Antiquity and the Middle Ages in the West. This was due to St. Augustine of Hippo, who was influenced by the early Neoplatonists Plotinus and Porphyry, as well as the works of the Christian writer Dionysius the Pseudo-Areopagite, who was influenced by later Neoplatonists, such as Proclus and Damascius.