I am currently active on BTCjam, but I would like to invest in startups too not just loans.
Thanks
It is not advisable to invest your bitcoins in shares and anything similar. Bitcoin gives you freedom of valuation, meaning it is rising its value day by day (recently crossed gold) which means you hold it in your wallet and trade/sell it for higher rate later on. If you want to increase your bitcoins then I suggest you to open up your own faucet and put some advertising on your page. There are many companies who will pay you for putting advertisement over your website/faucet. As you can see, people are crazy for earning bitcoins. Newbie's always start with faucet who are your customer's. For visiting you share as low as 100 satoshi's but earn like pot of gold!
FYI: It is good to be on safer side rather than being greedy. I would choose advertising way rather than risky shares.
We know that there's no risk-free in any kind of investment. It looks like Op asked about invest on startups project, the most famous is development projects of altcoins (ICO and crowdsale) but it could be end as big loss, right? My attention is heading to one coin : byteball. 2 advantages you may get.
1. Hold on your bitcoin as much as you want for long term investment
2. Get share from byteball according to proven balance of bitcoin in your wallet,
Look at byteball current price, it reach $57.62, fantastic, without ICO and crowdsale.