i am looking for mangas
where the protagonist ends up in a prarallel world
and has to grew in strength to surrive...

Not exactly parallel worlds in the beginning, but you would probably like Psyren

Dark Mage
ID He's strong though
Trump The story takes place in a parallel world where....
Crepuscule (Yamchi) He's taken to a new world
Tower of God Parallel world more or less...

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MuvLuv Unlimited and sequel

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stupid photobucket, wanting $400/yr just to display your images

if completely different worlds are also counted as parallel worlds, then yes. But if you meant with parallel worlds same world same characters different personalities, then I am completely wrong:
Ore ga Heroine o Tasukesugite Sekai ga Little Mokushiroku!?
No game No life
Hataraku Maou-sama! and Hataraku Maou-sama! High School!

and maybe the anime Mondaijitachi ga Isekai kara Kuru sou desu yo?. there is also a manga to it, but no chapter yet but Renzokusei scans plans to pick it up.

Some of these are just totally different worlds
Tsubasa: Reservoir Chronicle
Shiro Ari
Saver
Kyou kara Ma no Tsuku Jiyuugyou!
Tamago no Kimi.
Drifters

If you count the world of dreams as a parallel world, then Dreamland fits

wow thanks for all your help
I better get started =)