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Yes. You need to have 'liquid' STEEM. If your STEEM is powered up in your account, then it cannot leave your account unless it is powered down.

If you have liquid STEEM, you can power up to another user by going to the "Power Up" page in your wallet, and clicking on the "Advanced" mode. From there, you will be able to type in the name of the user you would like to power up.

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