The Prime Minister tweeted a series of pictures showing him handing out 'vote Boris Johnson' pamphlets around Ruislip Gardens station at night.
In one photo, Mr Johnson was shown handing leaflets to a driver sitting in their car in a queue of traffic.
He also pictured himself taking a photo with a constituent as he tweeted: "Out campaigning in South Ruislip! Polls close at 10pm - vote Conservative to #GetBrexitDone."
Several respondents to the post questioned whether Mr Johnson was concerned at losing his own seat in Uxbridge and South Ruislip.
No incumbent Prime Minister has ever lost their seat at a general election.
Mr Johnson is defending a majority of 5,034, with a strong challenge having been tipped from Labour.
One respondent to the PM's tweet questioned: "First ever mention of your constituency. Anything up?"
Sky News Australia breakfast host Laura Jayes tweeted: "Tory insiders are telling me Boris Johnson could 'genuinely be in trouble in #UxbridgeAndSouthRuislip'.
"Exit pollsters think the Lib Dem vote has collapsed there probably due to tactical voting for Labour."
Liberal Democrats leader Jo Swinson is another party head not guaranteed to hold her seat of East Dunbartonshire, with the 39-year-old holding a majority of 5,339.