How to attract students under Erasmus
Usually, Erasmus research projects are available to other students through network that your institution has with other universities. People who are responsible and actually paid to do promotion should be ERASMUS administrative officer at your institution, but if you for some reasons cannot rely on them, I suggest you to use ESN, ( Erasmus Student Network, organisation ) They can advertise and offer your vacancies to students,  this service suppose to be for free,
other way, maybe more time existing, is to contact collaborating universities from your network, and invite their students to take a look on your project.