Jelqing works for some, doesn't work for others. Also, you can damage your peen with improper technique, going too hard, griping too tightly, ect.. ect..

There's lots of penis enlargement gimmicks out there, you gotta separate what works from what doesn't. The stuff to avoid is pumps (temporary gains ONLY), pills (increase blood flow, temporary gains, lose all gains once you stop taking them), hanging (dangerous, puts too much strain on the ligaments making them harder to stretch thus negating effects).

In my experience, the best results tend to come from extender devices. These devices need to be worn for 1,000+ hours typically to see decent results (usually 1/2" to 1" gains are not uncommon). The problem is they are very uncomfortable to wear (downright painful at times). I have over 1,000 hours in one such device and gained 1/2" total. The gains where real because I stopped using the device for over a year and didn't shrink at all. Also my flaccid hang is much improved as well going from a "grower" to a bit of a "shower". No real gains in girth, extenders only really give length gains. And they don't work for everyone, some people log 1k+ hours with zero results, others gain 1/4th inch in a month, your mileage may very. It's very difficult to get 6-8 hours a day in a device when it's painful to wear, it's a large bulky object that is VERY noticeable if your trying to wear it incognito, you have to remove it for circulation purposes every 1-2 hours. Can't really wear it at your 9-5 job, so it needs to be worn at home really. Can't wear it while sleeping cause blood circulation issues could be very bad. They say no pain, no gain.

There's forums dedicated to an educated discussion on penile enlargement without psydo science and people trying to get at your wallet. Check out PE Gym or Thundersplace forums for the curious at heart. Real results from real people, source - I'm one of em.

TLDR; Extender devices work for most, but they are a bitch to wear! Is it worth 1,000 hours of pain for a measly 1/2" gain in length? Also, the bigger your dick is, the more you stand to gain. I started at 7" and am now 7.5" long. Someone with a 4" penis probably won't gain 1/2" in 1k hours.