You're are missing the "for", I think. "to search something" means "etwas durchsuchen" in German, while "etwas suchen" is "to search for something" in English.
- Er sucht sein Wörterbuch = He's searching for his dictionary.
- Er durchsucht sein Wörterbuch = He's searching his dictionary.
I don't know if it's really so strict, but that's how I learned it.