иска́ть

"искать" can take either the Accusative or the Genitive, depending on how definite the thing being sought is. The same alternation affects ждать, просить and требовать.

Accusative — a definite, concrete thing.

• Я ищу ключи. — I am looking for my keys.
• Она ищет работу. — She is looking for a job.

Genitive — an abstract quality or state.

• Он искал помощи у друзей. — He sought help from his friends.
• Он вечно ищет приключений. — He is forever looking for trouble.

Several of these are fixed: "искать помощи", "искать защиты", "искать повода", "искать встречи" and "искать приключений" are normally Genitive, and the Accusative sounds wrong.

Sometimes the case changes the meaning:

• Мы искали выход из здания. — We were looking for the exit of the building. (a door)
• Мы искали выхода из положения. — We were looking for a way out of the situation. (a solution)

With abstract nouns both often work, and neither is a mistake:

• Я ищу счастье. — I am looking for happiness. (neutral, everyday)
• Я ищу счастья. — I am seeking happiness. (bookish, suggests it may not be found)

Outside the fixed expressions above the Genitive now sounds bookish, and the Accusative keeps spreading. Negation favors the Genitive for a separate reason ("Он не искал славы").