Contact the employers that you spoke to during the fall by letter, email or phone. It is important to follow up with these contacts, especially if they are in the process of selecting interns. You don't want them to forget you just because they can't meet with you in person. It will be cheaper and more convenient. Use the lists of companies and alumni contacts that you prepared in the fall to inquire about opportunities.
Telephone calls are expensive and inconvenient.
If you have web site addresses, visit the sites and see if there is a way to apply for positions on-line. Follow up, follow up, follow up. Keep track of the contacts you have made and follow up at least once with each employer. Inquire about the timeline of the internship search process and take notes so you know when you might be hearing from them. Continue to look, using the same search methods but with more personal follow-up.