The phrase from 探す indicating purpose: 'in order to look for.' Used in expressions like 探しに行く／来る to mean going/coming somewhere to search for something.
新しいカメラを探しに電気店へ行った。
I went to the electronics store to look for a new camera.
彼は猫を探しに夜中まで歩き回った。
He walked around until midnight searching for the cat.
図書館で資料を探しに行くつもりだ。
I'm planning to go to the library to look for materials.