a virtue called "φιλοποητικῶς" which is translated as "in a way that makes friends" or "makes friends" or "makes and keeps friends" by various translators I've seen.
Here is something from a modern practical perspective, a very good YouTube video by a psychologist who gives very good advice, with regard to interacting with strangers, and which over time can lead to friendships in community, clubs etc.
Posting this here in this thread since it is about meeting and interacting with strangers: