user415: createrawtransaction is a bitcoin-cli command that generates a raw transaction given one ore more transaction ids and a list of Outputs, which are the destination amounts that will receive the funds.
AFAIK, The raw transaction is only based on the blockchain, and does not require any private key or address; the signing process is done separately, using signrawtransaction.
If the createrawtransaction process requires no secret keys, is there a way to generate a raw transaction online, using a web service?

user26873: That's correct, a private key is not required to use createrawtransaction. The private key is only required during the signing process of signrawtransaction just as you stated in your question.  
If you are looking for a web service that will allow you to create a raw transaction online, I suggest you check out http://coinb.in it does exactly this, as well as broadcast the transaction, and allow you to save a local copy to sign the transaction offline. 

user100526: I have created a step by step tutorial from create wallet to broadcast a transaction in testnet with online tools : step-by-step-create-and-broadcast-a-bitcoin-transaction-on-testnet 

415: <p><a href="https://bitcoin.org/en/developer-reference#createrawtransaction" rel="nofollow">createrawtransaction</a> is a bitcoin-cli command that generates a raw transaction given one ore more transaction ids and a list of <code>Outputs</code>, which are the destination amounts that will receive the funds.</p>

<p>AFAIK, The raw transaction is only based on the blockchain, and does not require any private key or address; the signing process is done separately, using <a href="https://bitcoin.org/en/developer-reference#signrawtransaction" rel="nofollow"><code>signrawtransaction</code></a>.</p>

<p><strong>If the <code>createrawtransaction</code> process requires no secret keys, is there a way to generate a raw transaction online, using a web service?</strong></p>
 26873: <p>That's correct, a private key is not required to use <code>createrawtransaction</code>. The private key is only required during the signing process of <code>signrawtransaction</code> just as you stated in your question.  </p>

<p>If you are looking for a web service that will allow you to create a raw transaction online, I suggest you check out <a href="http://coinb.in" rel="nofollow">http://coinb.in</a> it does exactly this, as well as broadcast the transaction, and allow you to save a local copy to sign the transaction offline. </p>
 100526: <p>I have created a step by step tutorial from create wallet to broadcast a transaction in testnet with online tools : <a href="https://medium.com/@athamidn/estep-by-step-create-and-broadcast-a-bitcoin-transaction-on-testnet-588daacc2b7a?source=friends_link&amp;sk=2c9a310c02801d09c667608d4651e80f" rel="nofollow noreferrer">step-by-step-create-and-broadcast-a-bitcoin-transaction-on-testnet</a> </p>
