Correlation between anorexia and mass media stereotypes
Short answer
According to a study dating 6 years back, the incidence rate of anorexia nervosa was stable over several decades.

Background
According to a review paper published in 2012, the overall incidence rate of eating disorders, including anorexia, was stable over the previous decades.  However, there was an increase found in the high risk-group of 15–19 year old girls, but that might have been due to earlier detection of anorexia nervosa cases or an earlier age at onset (Smink et al., 2012).

Given that the tendency nowadays is a moving away from the stereotypical barbie-sized waistlines I reckon above study is a valid source of information, as I do not expect the number of anorectic people to be soaring.  

Interestingly, while there are hosts of studies linking mass media and stereotyped ideal bodily proportions, a review study puts these findings in a different spot light. While the authors recognize mass media and eating disorders are linked, they question the size of the impact mass media has on these disorders. They did this by studying the correlation between social media versus negative body image and disordered eating in females (Levine &amp; Murnen, 2009). 

References
- Levine &amp; Murnen, J Soc Clin Psychol (2009); 28: 9-42
- Smink et al., Curr Psychiatry Rep (2012); 14(4): 406–14