Intercessory Prayer to Saints:
Rom 15:30 (join me by your prayers to God on my behalf)
Col 4:3; 1 Thes5:25 (pray for us)
2 Th 1:11 (we always pray for you)
2 Th 3: 1 (finally, brothers, pray for us)
Eph 6:18-19 (make supplication for all the saints and for me)
Tob 12:12 (an angel presents Tobit and Sarah’s prayer to God)
Rev 5:8 (angel offers prayers of the holy ones to God)
Paul is asking the people he is writing to, those believers who were then living on the earth, to pray for him, not people who have died and are in heaven.
Prayer to saints cannot be justified using those verses because they are not directed to or relevant to those no longer living on the earth, aka known as "dead people", but I've heard all the Catholic argument I care to about that.