This sounds very familiar. When brelatives are contacted, at first they seem really happy, saying they are thrilled, will always keep in contact and will call/email in a few days, then it never happens, they just stop everything without a word. ( Now, I do know that this happens with adoptees too)
For one, I think this is so cruel, to have us sit and wait for that email or telephone call, I would rather they let me know they have thought about it and think they are just not ready, anything...just answer us. I am going through this with one 1/2 sibling, he called me so excited and now nothing, it hurts.
I feel strongly though that you need an answer, is this just too difficult for your sister right now or what is the reason she's not answering you. Do you have her home address? Maybe you could write her a letter explaining how confused you are and could she let you know how she's feeling as you've not heard back from her.
Many of us here know exactly what it feels like to be the secret, it's a terrible feeling. I would probably try to get an answer from your sister first before contacting anyone else, having said that though, if she still doesn't reply within a reasonable time I would contact others in the family, they are your family too and may be very happy to hear from you, you just never know.
Sending you hugs...
