I am so sorry to hear Horace has gone missing
It is just horrible and as you have said you have looked but do not make yourself more poorly you have done what you can but do not loose hope. Horsfields are hardy little buggers.
As others have said they sometimes do come home as in Pagan Queens Herbie.
And my 1st tort was also found after escaping as in the link below.
http://www.shelledwarriors.co.uk/for...ad.php?t=70816
There is always hope and support from us all xxxx