Did not find him,
καὶ μὴ εὑρόντες ὑπέστρεψαν εἰς Ἱερουσαλὴμ ἀναζητοῦντες αὐτόν.
Luke said that now Joseph and Mary reversed courses. When they did not find him (καὶ μὴ εὑρόντες) among their friends and relatives, they returned to Jerusalem (ὑπέστρεψαν εἰς Ἱερουσαλὴμ) to search for him there (ἀναζητοῦντες αὐτόν). This was the natural thing to do. It probably took them another day to get back to Jerusalem. However, they were going to try and find him in Jerusalem, assuming that he was still there.