Most likely if you are with a lot of people you can manipulate the price without any doubts, and the fact is also that this already has been done back in the days.
I think there is a possibility to do this, so my answer is yes.
Yes we can manipulate the price of bitcoins if we are going to keep on demanding and supporting the usage of bitcoin.
But the ones who are able to manipulate the price of bitcoins are the whales, who are holding a lot of bitcoins in their wallets.
Maybe thousands of bitcoins or even millions.
A manipulation is only done by the minority who are holding a majority of share in the total circulation of bitcoins, with that for sure we cannot manipulate but they can, what we are doing is that we keep on buying so the price of bitcoin will rise for the benefit of everyone.