Today I was trying to hunt some DBs. I'm lvl31 and I killed bunch of lvl37-38 mobs. Got a few DB mobs but none of them droped DB So the event ended and I was left with nothing. Am I doing something wrong? Please let me know.

Dragon Ball hunting takes a lot of luck and tons more patience. Be diligent and you will eventually reach your goal.

Same here Baraniukas

Dragonball hunting is irritating, but so worth it when you finally get a full set. Takes some luck, and a LOT of patience.

Sometimes though, the best way to find something is to stop searching for it. When I'm having bad luck in a hunt, sometimes I quit for a day or two and just do quests during the hunt. A few days later, a Dragonball drops off a quest mob.

I read that you should not kill mobs five levels higer than you.

Kill mobs lvl 36

I'll keep that in mind.

Theres your problem it only works on mobs +5 and -5 of your level. Also stay in one area and keep killing mobs. Over time you will get dbs.

Does it necessarily have to be exactly +/-5 or it can be less too, like +/-3? Thanks in advance.

They have to be within five levels of yours, so yes you can. However, it is generally better to go for mobs that are at least three levels higher than yours. The reason being that you have a higher chance of a DB being dropped than if you were kill mobs that were weaker than you. Enemies that are also Super or Ultra have an even higher chance of dropping them so long as you're within the level range, but like I said it really depends on whether you're weaker or stronger.

Even then though, it still takes a lot of time, patience, and luck before you can get all seven. Generally, when I hunted for them, my top limit was four DBs per day with three being the average, and this was at lower levels.

Actually, that's false. At level 50 and 51, my friend and I hunted a level 60 chest in South Namek for Dragon Balls during a hunting period. After a few kills, a Dragon Ball actually popped out, so we proved that no matter how many levels a monster is above your level, you have a chance to get a Dragon Ball.

The opposite is even true; a guild member of mine, at level 36, killed those level 21 Dinosaur supers in West Yahhoy and managed to find a Dragon Ball. However, the chances for getting a Dragon Ball from mobs below your own level drop for every level you are above the monster. It decreases at a rapid rate, so you would have to be extremely lucky to get one if you're too many levels above a monster.