Snape curses himself.  Curses himself for the role he must play, and curses himself for causing such abject misery to blossom forth in those green eyes opposite them.  

The panic that is created after Harry reveals himself to be a Parseltongue is almost more than he and the other professors standing by can manage.  It is little surprise to find that the boy--the current ward of Hogwarts--has disappeared into the crowd.

After sending his students back to their rooms, he makes the first sweep of the castle, followed shortly by his fellow heads-of-houses.  Minerva starts at the top, while Flitwick does the same to the other side of the castle. Sprout handles the middle and he is left with the dungeons.  

He wonders too many times what he will find when they finally discover the boy.  Will he be fine? Puzzled that they have searched all over for him?

He would like that to be the case, but he fears something far worse.

The longer it takes to find the child, the more that fear grows within him, until it is all he can feel.

Both Filius and Minerva report that the boy has not been seen on any of the towers open to the air.  That there will be no mangled little boy bodies to clean up at the base of those towers is a relief, but not a long-lived one.  

Pomona reports that the boy has not been seen in infirmary or the kitchen or the library.  

Hagrid is always traversing the grounds, and he knows that the large man will tell him should he come across anything out of the ordinary.  It is a trip he is glad not to make.

The dungeons get colder and colder as he checks every nook and cranny that he can think of to look in.  

As it happens, it is purely accidental that he finds the boy.  He literally trips over him in a dimly lit corridor that has not seen the light of day in some centuries.

Harry still has tear tracks on his cheeks.  This he notes as he gathers the far too quiet, far too cold, child into his arms and makes with great haste back upstairs.  He sends out a patronus to Pomfrey, telling her to alert the others and to meet him at his quarters.  He isn’t certain that the boy will last much longer, and his quarters have the same potions that one would find in infirmary.