According to an eyewitness, the two were behaving like loving couple, reported E! Online.
"They were acting very much in love, she kept hugging him. Their love looked genuine," the eyewitness said, adding that the two laughed a lot at one another.
The birthday weekend comes after Efron and Miro were spotted in Denmark enjoying some shopping and fine dining.
Previously at an occasion, Efron was reportedly overheard introducing Miro to a fellow patron as his 'girlfriend'.
Prior to that, they attended a Los Angeles Dodgers baseball game and even enjoyed a double date with Dylan Penn and a male companion.