Hi there! I found this document on airbnb's website, and it helped me determine whether my income was taxable or not, based on how my apartment was used for renting:
http://assets.airbnb.com/eyguidance/us.pdf
I have not received a 1099, but did get an email saying "tax inforamtion was ready," however the link did not work. I only rented for 14 days last year and my gross income was nowhere near the $20k minimum airbnb has set to receive a 1099. As far as I know, this document should help you determine if your income needs to be reported still or not if you do not receive a tax document.
Hope that helps!
Justin