As published in the PHB, his type changes to Animal, but it will not break a Hold Person spell - he was a valid target for the spell when it came into effect, and subsequently changing type doesn't change that.
However, the most recent errata to Wildshape change the ability so it is based on the Monster ability 'Alternate Form', instead of the spell Polymorph; once this change is applied, Wildshape no longer affects your type. You'll still be a humanoid (human) (or whatever), and Hold Person will remain in effect.
-Hyp.