Buy a replacement MagSafe female chip for the MacBook Pro

You might want to check your power adapter's plug as to whether the debris stems from there. If the plug is all right, I'd just remove the debris and not worry any more about it.

iFixit is a good place for parts. They seem to sell complete screw kits for different models.

Although one screw missing won’t hurt the unit. I repaired a machine recently that is literally held together with celo tape and stickers.