Tex. R. Civ. P. 758
If the plaintiff, his agent or attorney, at the commencement of any suit, or during the progress thereof, for the partition of land, shall make affidavit that an undivided portion of the land described in plaintiff's petition in said suit is owned by some person unknown to affiant, or that the place of residence of any known party owning an interest in land sought to be partitioned is unknown to affiant, the Clerk of the Court shall issue citation for publication, conforming to the requirements of Rules 114 and 115, and served in accordance with the directions of Rule 116. In case of unknown residence or party, the affidavit shall include a statement that after due diligence plaintiff and the affiant have been unable to ascertain the name or locate the residence of such party, as the case may be, and in such case it shall be the duty of the court trying the action to inquire into the sufficiency of the diligence so stated before granting any judgment.
Tex. R. Civ. P. 758