The first thing one has to understand about the Stack Exchange family of sites is that they are question and answer sites, not forums and not bug report platforms. There is simply no point whatsoever in informing the world that I have the same problem. On bug report sites, the number of people affected by a bug is a useful tool when deciding what bug to focus on. On a Q&A site, the number of people interested in an answer is irrelevant.
So, there is no way and there really shouldn't be any way for anyone to indicate that a problem also affects them. It's simply not in the remit of the site. It is kind of like wanting a "I was wondering about this too" button on Wikipedia. What would be the point?
The only real problem I see here is when a question has been asked already, but there are either no answers or none of the existing answers help the new user. In the second case, the solution is to post a new question, referencing the old one and explaining that the solutions offered there didn't work (also explaining exactly how they failed). For the first case, where there are no answers, it is reasonable to write something like "I know this has been asked already here, but that was months ago and there have been no answers. I am therefore posting the question again in the hope of reviving it." Then, the old question can be closed as a dupe of the new one and the new user might have a better chance of getting an answer.
These are relatively rare cases though. The most usual situation is that a question has been both posted and answered so there is nothing the new user should do. There would be no benefit from a "I had this question too" button.
