Lots has changed since 2011 particular now with whatsapp groups, communications in general and now platforms like Freetrade, so the question is for example if 100,000 small investors sold £100 of shares on the same day in one company, would it move the market like institutional investors do?
It depends on a whole range of things like market size, how many buys are happening at the same time, liquidity of the stock etc.
100,00 * 100 is 10 million so if you did it for Amazon it wouldn’t move the needle.
If you did it for a AIM company, the violent swing will more than likely cause the stock to be suspended.
I cannot find any details on what triggers AIM shares to be suspended but RBS shares were suspended when they dropped by more than 8% in 2016, this was caused by Brexit. In this case there was billions of £’s of shares sold to cause this.
As @saf outlined, purely depends on the market cap. I doubt that small AIM company will attract 100,000 investors to transact within a day, purely due to low awareness.
Your numbers would represent transactions totalling £10m. Considering the LSE companies’ total market cap is about £4tn and there are 2,600 of them, it is roughly £1.5bn per company.
£10m of intraday transactions would represent mere 0.67% of the total value, hence will essentially make no effect considering that 1% - 5% daily swings are a norm.
Therefore, most impact is made by institutions: pension funds, sovereign states’ national savings, other mutual funds and corporations storing their cash in the market. Individuals simply cannot be more impactful.