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.
Add to that those Chinese miners, it seems that the bulk of bitcoin comes from them.They have millions being hoarded and it seems can change bitcoin price it they all unite.If we all unite, then we can manipulate bitcoin price but it will seldom happen. last time maybe is due to halving?