Secondly, I will advise that you include every member taking a loan to have a surety to vouch for him, this will make him responsible over any abscondment or default,
Nobody is going to do that and it would effectively mean the lenders would go out of business on the forum, i'm sure they don't want that. How do you stand in as surety for someone over the internet and risk your account based on their own actions, doesn't make any sense.
I can see this loan defaulting challenge is not good for the service and can bring one down to bankruptcy if it persist in such manner.
That's the risk any lender bears in a no-collateral loan. You lose some and you also gain some, particularly if the interest charged is 'high'. I am sure if they were any close to bankruptcy, they would have stopped borrowing, so it is safe to say that it is still profitable.