Sorry to hear about your predicament. I don’t think external investors are an option – they are almost impossible to find even for successful services companies because exits are so difficult.
Agreed that this is a tough market, but I would recommend some soul searching. You must decide whether you are better suited to running your own agency or working in a job. Running an agency has a business angle that many professionals can find hard to handle.
How much work have you done in these 4 years? If you come from large agencies, you should have an established network. Are you targeting the right clients? Is there a mismatch between how you see your capabilities and how clients see them?
Why are your existing clients not giving you more work? Are there any quality issues?
I do know that managing cash flow is the hardest thing for an agency. Was financial management the problem?
Only by asking yourself tough questions, will you understand the best way forward. If you still feel you want to run your own agency, then understand what went wrong and ask if you will be able to fix it the next time around. Spend the gap time building a network of potential clients and filling gaps in your capabilities. If not, look on this time as a rich learning experience and go back to a job. You will find that you are much better equipped after your entrepreneurial journey. There are no rights and wrongs –ask the questions, think about the answers and do what what makes most sense for you and your partners. Good luck.