Stack Exchange's built-in search is limited to questions and answers. Comments are second-class citizens by design; they're not meant to have information with any lasting value, which is why SE developers don't put any effort in making them more searchable.
You can use a web search engine, such as Google. On Google, add
site:math.stackexchange.com to limit the search to this site (including meta); other search engines (yes, they exist) tend to have a similar capability. For example,
orangutans site:math.stackexchange.com finds your comment (and will find this meta thread soon after I post).
If you know who posted the comment, you can look at that user's comment activity (sorted by date). For example, these are your recent comments.
If you still can't find the comment you're looking for, you can turn to methods that involve a bit more familiarity with computers, if not outright programming.
The Stack Exchange API allows a number of queries. In particular, you can search for comments within a date range, comments on a given set of posts, or comments by a given user (optionally restricted to those addressed to a given user). You can retrieve up to 100 results per query (specify 100 as the value of the
page parameter), and use your browser or a text editor's search command on your computer to locate the precise comment you're interested in. For example, the URL
http://api.math.stackexchange.com/1.1/users/7850/comments?pagesize=100 retrieves your 100 most recent comments; the next ones are at
If you don't remember who posted the comment, and it's not a very recent one, then you can turn to the Stack Exchange data explorer. This is a read-only copy of the SE database, updated roughly once a month. Searching it requires knowing some SQL (specifically Transact-SQL). Browse existing queries first. There is already a query to search through all users' comments. Note that the search is case-sensitive, so you need to search
rangutan, you won't find your comment by searching
orangutan. You can use the character
% to stand for any substring (e.g. a search for
Or%tan finds many comments including that Orangutans one), and
_ to stand for any one character.