Sorry to hear about his tail ripping further, honestly it's not that surprising. The good news is bettas "CAN" and I emphasize can regrow their fins just amazingly. That being said, they often do not look the same, or as good as they originally did. Clean water is the first step. Keeping them at a nice, stable temperature, preferably at 78-80, helps. So does the use of tannins and API stress coat (at least I've had good experiences with it). Like any fin regrowth you want to give him a high protein diet to help. Smaller meals fed throughout the day is the best bet. From what I've seen Live > Frozen > Pellet > Flake > Freeze-Dried. Some people will argue this point, but what is agreed is a high protein food (at least 42%, preferably higher) is vital. If you feed a pellet or flake, look for something that has fish as the first ingredients, not wheat or any other filler.
Some people really try to avoid using the net, but it can't always be helped. I've heard that if you let it sit in his tank for a minute before you try to catch him will let it "soften" up. This may be absolute garbage, but it's worth a shot.
If you see any clearish or slightly whitish where the wounds are that is usually new fin growth, it may (usually will) colour up later. However if it looks like white cotton it's another issue (but hopefully nothing to worry about).
It can take anywhere from a few days, to even a month or more to see new fin regrowth, it all depends on the fish, his health, and sometimes a bit of luck.
I hope your boys tail starts to get better, keep us updated.