I think your examples would be understandable to contemporary speakers of AmE, but they are usually reserved for objects with forgotten identities. That being said, comments and synonyms of the terms below have shown me that there is a lot of carryover from object name placeholders to those for people. This is probably due to the fact that the person’s name itself could function as the forgotten object.
Some commonly used alternatives are:
- also: what’s-his-face with the same meaning, but more casual/irreverent
- These two are very common
- The phrase is treated almost like one word. When written, the spaces are usually removed or replaced with hyphens. The pronunciation also shifts. The "h" becomes silent, the s merges into the next word, and everything flows like one word. The stress is on the first syllable. What'siz-name, what'ser-name, what'siz-face or what'ser-face.
- Mr. ‘S’-something
- Another common tactic is to vocalize whatever scraps of the person’s name you remember, interspersed with instances of the word “something” for missing parts
- This can be combined with intentionally unintelligible mumbling, extending the last sound of the portion your remember (Mr. Smmm. . .), or include guesses that you know sound similar to the intended name even though you know they are wrong, such as Mr. Smiley or Mr. Schmidt
- This one doesn’t really fit for your example, but would be used in cases where the speaker doesn’t care what the person’s name is or deems it irrelevant to the statement
- This has been used as a euphemism for stronger insults in the past, so it is occasionally used these days as a form of quaint derision: You old so-and-so!
All of these are informal, and can be humorous in the right context.
As for which is the most common, my guess would be what’s-his-face—based solely on my own experience. This is also the least formal option on the list, so maybe it makes sense that I would hear it more than the others during the informal conversations that permeate my informal American life.