I say, and with God's success: It is not permissible for him to perform tayammum before searching; because it is a condition for the validity of tayammum to search for water if he thinks it is nearby. He must search for it within a distance of a "ghalwah" — approximately 150 meters — if he thinks it is close, otherwise it is not required. The method of searching is to look to his right, left, in front of him, and behind him within a "ghalwah". He is not obligated to walk; it is sufficient for him to look in these directions while he is in his place. This is if there is nothing around him that obstructs his view. However, if there is a small mountain or the like nearby, he should climb it and look around, provided he does not fear harm. See: Al-Bahr Al-Ra'iq 1: 168, Al-Durr Al-Mukhtar 1: 230, Sharh Al-Wiqayah p. 112, Al-Muhit Al-Burhani p. 281, and God knows best.