Just tested it and it works fine for me. Make sure the webpage has fully loaded before hitting that button. Works fine for me in Firefox 46.0.1, this morning with 58.0.2, and IE 11.192. Haven't had any issue previously with Chrome currently showing as 63.0 and *shudder* Edge which I can't launch for some reason.
It would be a plus if you mention the browser and version you;re using, the url of the page you;re trying to search from, and which of the two search buttons you're trying to use as they search different purposes.
To search the general forums, make sure you're doing it from the front page here:
https://www.gog.com/forum/general To search the forums, make sure you're using the search button shown in the image I've attached to this post. The one along the top is for the game portion of the website.
If you're in one of the threads, the search will only work for that thread.
And of course there's always this as a back up:
https://www.google.com/search?q=site%3Agog.com%2Fforum%2Fgeneral%2F+pause+downloads But to answer you;re question if the search above doesn't make, we need to know how you;re downloading your files. Galaxy? The old downloader? Manually? Again details are a plus.
Hope this helps