I have a valid ESTA since February 2014 which is valid until 2016. I used it last month to visit the U.S. for 2 days. After that I applied for a B2 Visa to stay with friends for 1 year which has just been denied. Can I still travel to the U.S. with my current ESTA for a holiday of 2 weeks in the upcoming period?
ESTA is a pre-approval to enter the US under the Visa Waiver Program (VWP). It does NOT guarantee entry to the US, and all of the criteria of the VWP still apply at the time of entry.
One of the requirements of the VWP is that it can not be used if you have been refused a US Visa in the past.
Thus despite holding a (potentially) valid ESTA, you are not elligible to enter the US using the Visa Waiver Program. The only way that you will be allowed entry is to apply for a Visa, and hope that it is approved this time...