Here is a quick patch to restore searching by topic back to Spaz HD. Apparently Twitter has removed the old search API Spaz used and put it at another address. This patch adds that address and redirects the client when searching to that new address.
Note: It seems this app has been abandoned by its developer, as all the repositories I've tested that were linked from Spaz's home page were removed. I still think Spaz is the best free Twitter client for webOS, and trumps over the clients that exist for pay now.
Note 2: Neo is based on SpazCore, so this patch can be easily modified to patch Neo as well. I'll leave that as an exercise.
Note 3: This patch will not be uploaded to Preware, as Spaz does not come with webOS and the patch portal only accepts patches for apps that ship with webOS.