There are three problems I can see here:
1) If my memory serves me well (and I don't have a chance rn to verify it easily), TODO panel is for project's TODO; what you need is another panel: Code Explorer.
2) Part of Code Explorer panel for showing TODOs is rather... shy and you need to wait (or switch to another document and go back, or reload your document) for your TODOs to appear; sadly, there is no visual hint that a document is being scanned for TODOs, NOTEs and whatnots (yes, I have filled feature request

)
3) You could wait very long for your TODOs to appear in Code Explorer panel, though, and they wouldn't, because they should go inside comments, and in PowerShell you need to use # (or <# .. #> for comments, not //.
Hope that helps.
BTW, I can see there are some bugs with parsing of TODOs in PowerShell:
gives TODO level 1, as expected, but
shows level 2 (same goes for 3 and... 33).
on a last line doesn't show at all.