When they were new, they ran everywhere for a couple years. They were more powerful at 3200 horsepower actually than the worn out F40s then in use, although only 12 cylinder version of the GE power plant that runs 16 bangers in freight and P40/p42 passenger types. When the P40s started showing up the P32s tended to go into push pull commuter service, particularly in Michigan and California. Two were actually put in Amtrak California service and got CDTX road numbers. The others in the 500-518 Amtrak road number group received the modified blue paint scheme with the white stripe.
As the previous posts have indicated, the present status is mostly for switcher use at various terminals, and commuting in California. Three at least have now been overhauled and repainted again. Two are still in long distance road service, as 507 and 509 are regulars as third units on the Coast Starlight and move up and down from Redondo, where they are maintained. Often one will be seen in Portland for a while, and/or Seattle. Recently there have been combinations of a P32, a P42, and an F59 on the Starlight, which is most cool.
The Crescent and the City of New Orleans occasionally swap out a unit between Chicago, New Orleans, Washington, and/or Beech Grove, but only rarely, about 3 or 4 times a year. There may be one at Sanford working for the Auto Train Terminal, and as a previous post mentioned, Jacksonville used to have one. I am not sure whether Miami has one any more or not. But the only Silver move would be if and when a Sanford, Jacksonville, and/or Hialeah unit swaps out or fills in for an ailing P42. The return of a second unit to the Silver trains has helped, because now more newer engines are found in Florida at any given time, and that gives Amtrak some additional flexibility in case of breakdowns.
Besides California, the best place to see one is, as mentioned, Chicago...there is almost always at least one working the Washington/Wilmington beat.