Guys never talk to me alone?

Therare several guys at work who only talk to me when a bunch of people,are around. not only dio they talk,but they tease me alot n joke. When Im alone with them one on.one, even if I look at them , ,they act like Im diseased and they're nkt friendly at all, which is completely opposite. What are they trying to prove? Tgis,happens,alot to me. What do I do?