London Baptist Confession:
chapter 26; paragraph 11. Although it be incumbent on the bishops or pastors of the churches, to be instant in preaching the word, by way of office, yet the work of preaching the word is not so peculiarly confined to them but that others also gifted and fitted by the holy spirit for it, and approved and called by the church, may and ought to perform it.
I believe that a person should be sent out by the church for things such as open air preaching, teaching classes, etc. However, your average Christian is called to witness to people in their life such as family, friends, co-workers, waitresses, etc.
The quoted chapter from the LBC does not forbid the average Christian from giving the Gospel to their neighbor or to a guy sitting next to them on a bus.
I simply quoted the confession to remind ourselves of what we all agree the word 'preach' means. Invariably, these discussions go nowhere because of equivocation on the word 'preach'. Since we are a Reformed discussion board we ought to discuss things, as much as possible, using Reformed definitions. When we discuss things with non-confessional people we might, of course, use the word 'preach' in many different ways, but here we should stick to the confessional definition.