To follow the above explanation:
>>What we are looking for (is / are) these people.
>>What I want to find (is/are) three pencils.
Correct me if I’m wrong ,'gals 'n' fellas' :)haha.., but this is a perfect example of ‘psuedo wh-clefts’ ( as opposed to ‘th’ and ‘it’ clefts) where the first part , ‘wh-phrase’ ,takes a subject position and being quote,‘normally a nominal relative clause’, unquote , at the same time.
It is linked with its focused complement by the verb BE , here ‘these people’ and ‘three pencils’ are the noun phrases and their plurality has no bearing on the form of the verb BE.
We can also extrapose the wh-part accordingly :
‘It is these people what we are looking for’, but ‘ These ARE the people (what,-not that)we are looking for.
‘It is three pounds what I want to find’ , but ‘ Three pounds IS what I want to find’.
Well,I guess I muddled the asker rather than helped.If so, forgive me please.:)
p.s. At least you know now why it is ‘IS’ there and not ‘ARE’.