Most people check email and respond to private messages first. When the person later finds out that the message was also publicly posted, don't be surprised to find that the public response is not as sympathetic the second time around. If someone sends you a private message, it is a breach of confidence to announce it or post a public response. An exception to this might be an informative response from a company and manufacturer that clarifies an issue for the group. Even so, it isn't likely to inspire trust.
Interaction Give a message time to propagate.
Don't repost becasue you can't immediately see your own message. Many servers are connected to the backbone of the net and messages can sometimes take days to arrive if a server goes down or gets blocked for some reason. For those who crave interactivity and immediate response, there are chat boards, IRC, email, and live conferencing tools. Those channels may provide instant gratification, but they never have the quality of content that is possible when someone takes the time to consider a question and provide a well reasoned response. It shouldn't need to be stated, but support groups are not the right place for insults, racism, name calling, character attacks, product promotion, tantrums, tasteless jokes, spelling lessons, fantasies, fetishes, test messages, international politics, editorials on current events, ranting, sarcasm, reposted jokes, investment tips, theological manifestos, etc., ad nauseum.