What is the ruling on the actions of a young man who contracted marriage (nikah) with a girl and went out with her, but the marriage was not officially solemnized due to her family?

What you did in contracting this marriage is invalid, reprehensible, and an infringement upon the rights of the girl's family, because it lacks the condition of a guardian (wali). This is based on the Prophet's (peace be upon him) saying: "There is no marriage without a guardian," and his saying: "Any woman who marries without the permission of her guardian, her marriage is invalid," and his saying: "A woman may not give another woman in marriage, nor may she give herself in marriage." It is incumbent upon you to divorce this girl and sever your relationship with her immediately. It is not permissible for you to touch her or be alone with her. If you wish to marry her, you must approach her guardian and seek marriage from him.