Own some but like said in BTC thread, i'm quite conservative with my investments, not really look any day trading or huge pump in prices as i don't see myself to be very good in that game which is played by all huge financial institutions and their full time research dudes which i at least hope (have some pension funds which are not in my control....) have better understanding and tools to study these companies and possibilities etc... yes i can make some simple researcs but guessing if some P/E ratio is good or undervalued or what so ever for particular company is much guessing for me than my horse betting (where i also sometimes get it right)
Most what i own and keep buying monthly are boring big companies which i believe keep doing good and they had, no that kind of huge winnings like in speculative ones but when target is save, you usually are happy to much smaller profit than in gambling, something around 10% sounds really boring and almost nothing but after some time you can see how that amount gains compounding interest and in 20+ years your monthly savings might have gaine quite nice pension fund and that doesn't need any big capial at any stage, if just can put side something all the time, can be under €£100/month and even half but once capital is big enough, that even small % annual increase is quite a big amount.
Of course i also as hobby to buy some penny stocks, but these then are total different and taking them much more like any form of gamble and there always are these companies who make themselves worth a lot with some great invention or any other way which nobody could see beforehand, Unfortunately there are very few of these succeed for long term but like you been mentioning, these can gain value really fast, of course some huge increase in value can be really short and drop faster it raised so need to always think if it's sustainable or something you wanna hit withdrawal button after certain increase.
Other similar hobby are also non listed companies where you can participate to crowdfunding type of investment when you buy something which is not listed, often startups who are raising money to get their product out etc.. Like to follow some of companies i for some reason thougth might be successfull in future, these of course often end up to be nothing but like in penny stocks, it's extra high risk investment with high risk and high reward, wouldn't add any huge amounts to these but often can take part with something starting from $1000 which is not that huge money if been saving and investing long time, it can fit to your risk appetitate and some can return huge ROI, but never invest in these if not thinking business plan and roadmap have good potential.
As we are in gambling forum, funnily one of best performed investments i have in last 15 years have been igaming related, many companies collected funds to launch their products, many also were quite low valued even they were already listed in stock exchange and it's not really mission impossible to sometimes get it right how some gaming company gonna do in future, i've seen many people writing here very good thoughts about some companies futures which have been well educated opinions from people who use products and know business and competitors, many predictions here have been happening
Then there are these things were market just get everything wrong, especially in these days when whole world get word within few hours, this as one good example when Elon Muskot tweeted "Use Signal" (which have come more used after Whatsupp T&C:s etc...) and people started to by shares like crazy, unfortunately just from wrong company, Signal is made by non profit organization and not listed, can just imagine how this Signal Advance owners and founders feel when saw how much their company gained value from nothing
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In a couple of others that they keep saying could explode maybe this week.
A new President is bad? Or what happened to most of the stocks today?
When enough people (or enough money), these kind of "bit" speculative values can be made, it's not more complicated than any other market, supply and demand, buy something and get enough others to do same and enjoy their money who entered there bit too late. It can be attractive way of gamble, but like said, day trading is not my cup of tea, i don't believe me getting rich fast happen in this world anymore 
