I use google

"M_N_A" site:http://ths.gardenweb.com

ya that would work. but some author has an ID that's common English word, which will return gazillions of hits...I am surprise search by ID feature is not available...

You could search the forum for the username. There's a search box at the bottom of the main forum page.

At the top of the main page it says:

"Before posting a question, please check the FAQ and do a search to make sure it hasn't already been answered."

Click on the word "search" to search this forum or all forums.

i had tried the search box. If I put M_N_A there, the returned links are not related to me at all, let alone if i would need to search for a user with common word (say, "house")

Put in MNA

If you don't find much it is because the database is incomplete and the software poorly written.

Try doing a google phase and site search combined.

"posted by M_N_A" site:ths.gardenweb.com

Here is a link that might be useful: relevant threads