In the past I have used both Probux and Neobux with little success, but finally I came across a PTC that actually makes me some profit. It is pretty simple to get started with it too. At the moment I am making $5 a day with 520 refs.
Here is a quick guide to help you started:
1) Signup to Ojooo
wad[.]ojooo[.]com[/]register[.]php?ref=tharek
2) Upgrade to a premium+ (30 day) and buy 200 or 300 referrals.
3) Buy referrals every 3 days (you can either fund your balance more or just use earnings).
4) Repeat step 3 until you reach the limit, then upgrade to VIP, repeat step 3 and so on.
Average earning per 100 referrals is ~$1 a day. So you can make quite a bit of profit per month. Obviously, to make a lot of profit you will need to reach the limits of 3000, 5000 and then 10000.
TIPS:
Do not recycle - Referrals are recycled by the system every 3 days for free.
Don't forget to renew - Don't forget to renew the membership or almost all your referrals with disappear.
Keep buying - I know it is tempting to cash out earnings, but it is better to spend it on buying more.
Renewing/extending - From doing research I have learnt that it is better to just let your referrals expire, as there is no fee and just buy new ones. This makes it cheaper than autopay or extending (unless it is for 90 days).
If there is any confusion I will try my best to help you out,
Best of luck.