I have noticed that sometimes some news resource will publish an article about a particular ETF, it gets attention and a lot of other news resources will publish the same article. Does it attract the additional demand for this ETF though? If more people see it recommended, doesn't it inflate the price for it? And then once attention fades away weeks later the price would go down?
Publicity can cause people to invest money into a fund. That mean that the size of the fund will grow, but it doesn't necessarily mean the fund price will go up because of the additional money.
For example with an index fund almost all the money will be invested into the companies that are in the index, very little will go towards the fixed and variable expenses. The price of each mutual fund share will not move, unless the value of the underlying investments go up.
For a non-index fund part of the expense is to cover the cost of the staff that will decide where to invest the money. The more money flowing into the investment the more money available to pay this expense. But again the shares of the fund shouldn't change.
Non if there is a large outflow of money it can make it difficult for the fund, because they might not have enough money to cover their expenses without raising their expense ratio.
Now if we were talking about individual stocks, the publicity can cause the price for a share to rise. Later when the opinion changes the value of the stock can go down.
If the money flowing into a fund did cause it to go from a multi-million dollar fund to a multi billion dollar fund overnight, it could make it hard for a company that was supposed to be invested in small companies to run out of places to invest. That could change how the fund performs against their benchmark.
The creation and redemption process for ETFs allows arbitrage to take place by the authorized participant (the bank that buys the underlying securities to create ETF shares, and vice versa), which should keep the ETF's price close to the net asset value (NAV) of the underlying securities by arbitrage.
Essentially, the authorized participant is the only entity allowed to create and redeem ETF shares, and they trade the underlying securities to manage supply and demand for the ETF shares. If there's a price deviation, they can buy/sell the underlying and redeem/create the ETF shares to capitalize on the arbitrage opportunity.
Price dislocations do happen, although they are often small in magnitude (basis points) or very short-lived (lasting minutes). ETFs with less-liquid underlying securities tend to be at a higher risk to stray from NAV since arbitrage can take longer. The August 24, 2015 flash-crash is an example where a huge dislocation happened in large, liquid ETFs and "some ETFs flirt[ed] with 50-plus-percent losses—all while the S&P 500 registered a 4 percent decline."