I have a friend whose son still lives at home with him at the age of 29. His son has a disease called Crohns Disease. This is a very disabling disease hence his ability to work is very limited. My friend provides him 100% support in the way of food, room and board. In addition he pays all his bills including his insurance costs and medical cost.
I have researched but can not find where he can write him off as a dependent or get any type of tax credits. Any suggestions? Am I missing something?

I suspect you've missed something. At a minimum, your friend should be able to deduct his son's medical expenses since his son should be a "qualified relative" for that purpose. (See IRS Pub. 502). If the son is "permanently and totally disabled" (probably not if can work at all) then he is a "qualifying child".

If he's a qualifying child, then the father can take a dependency exemption; if a qualifying relative, the father can take the dependency exemption only if the son has less than $3700 in gross income. (See IRS Pub. 501).

If the father is single, he may qualify for Head of Household filing status.

Ira