1 Thessalonians 3:9-13 English Standard Version (ESV)
9 For what thanksgiving can we return to God for you, for all the joy that we feel for your sake before our God, 10 as we pray most earnestly night and day that we may see you face to face and supply what is lacking in your faith?

11 Now may our God and Father himself, and our Lord Jesus, direct our way to you, 12 and may the Lord make you increase and abound in love for one another and for all, as we do for you, 13 so that he may establish your hearts blameless in holiness before our God and Father, at the coming of our Lord Jesus with all his saints.

This was Paul's response after hearing Timothy's report on the state of Thessalonica.  While Paul prayed for God to make a way for him to return to Thessalonica himself, he also prayed for their 1:increase in faith (or what they were lacking), 2:to increase in love for one another (The church of Thessalonia was not a loveless church, but like most, still have room for improvement), 3:established blameless in holiness (set apart from the world), Paul was remembering Jesus' return could be today and wanted them ready.

When was Paul praying-- "DAY AND NIGHT" how about you?

How-- "MOST EARNESTLY/EXCEEDINGLY"  this double compound is probably the most emphatic of all

He wasn't praying for himself, but yet, others..and in love. The love of others.