Where is the Immigration Office in Bangkok for a Thai Tourist Visa Extension?

I am NOT 100% sure but I think you need to go to this location to get a 30 day extension on a 30 day visa exempt entry stamp

okay I think you don't have any visa in your passport. :O

You would have needed to buy a tourist visa from a thai consulate in another country before you came here

If I read correctly you showed up here and were stamped in free for 30 days :O <- that's not a tourist visa that's a 30 day visa exempt entry stamp.

For extensions on 30 day visa exempt entries I believe you use the new location at the Muang Thong Thani (where they moved section K <- the section where they do 30 day extensions).

It's at the government complex on Chaengwattana Road Building B Second floor South entrance.

Immigration Bureau (Sub-Div.2, Imm. Div.1) (Building B)

Address: Chalermprakiat Government Complex, 120, Moo 3, Chaengwattana Road (Soi 7), Thungsonghong, Laksi Bangkok