On behalf of second lieutenants everywhere (Air Force in my case), thank you and all the other non-coms who taught us how to be officers. I know in my case, the lessons my sergeants taught me, and the attitudes and habits they helped me develop, have served me very well throughout my life (I'm now 61.)
Have you tried asking your Sierra Club friend if he'd be interested in doing some short weekend trips?
Another source might be the local gear shop (not the big-box like REI.) Quite often, mine will "sponsor" weekend trips in the sense that they'll come up with a place to go, a date, arrange the car pool, and perhaps send someone (with appropriate certifications for first aid, etc.) from the store along as a guide. They don't charge for it, but "offer" to put together a food package from the store at a discounted price. They do it hoping to build business. It works well for them, in my case, and it has also worked well for me. I went from no hiking buddies to two hiking buddies over the course of two store trips to a nearby metropark that just happens to have a 30 mile backpack trail (in OHIO!!)
By the way, I used to do quite a bit of solo hiking and I'm now more comfortable with a companion. It's not a fear factor, it's just that what I want out of a trip has changed; I find I enjoy company more now. The bonus is that my wife (also a non-hiker) is also more comfortable about my going if I'm with someone. I suspect it may be that having a witness makes it quicker to obtain the life insurance check.
I'm sure others from your area will have more specific information about other hiking groups.